From: "Luis R. Rodriguez" <[email protected]>
Bjorn, this v6 respins the introduction of pci_iomap_wc() and
its users onto Bjorn's pci tree [0] on the next branch. It goes
with your own Acked-by on the PCI part as well as the framebuffer
subsystem maintainer's own Acked-bys for the framebuffer driver
specific changes.
The driver changes are being submitted through the PCI tree
to make the caller have users as soon as its merged otherwise
we'd have to wait 2 release before full integration.
Bjorn, if you rather pull instead of apply these patches one
by one I've put these changes up on a branch on a tree based
on yours to pull from.
The following changes since commit 9b08ae0dde00c20a75cf15636a08e0901c6fe482:
Merge branch 'pci/msi' into next (2015-05-08 15:05:10 -0500)
are available in the git repository at:
https://git.kernel.org/pub/scm/linux/kernel/git/mcgrof/linux-pci.git pci_iomap_wc-v6-20150520
for you to fetch changes up to 480d550fa62bdad1c8f25b16d27d2035f36a283b:
video: fbdev: vt8623fb: use arch_phys_wc_add() and pci_iomap_wc() (2015-05-20 15:12:04 -0700)
[0] https://git.kernel.org/cgit/linux/kernel/git/helgaas/pci.git/
Luis R. Rodriguez (4):
pci: add pci_iomap_wc() variants
video: fbdev: arkfb: use arch_phys_wc_add() and pci_iomap_wc()
video: fbdev: s3fb: use arch_phys_wc_add() and pci_iomap_wc()
video: fbdev: vt8623fb: use arch_phys_wc_add() and pci_iomap_wc()
drivers/video/fbdev/arkfb.c | 36 ++++--------------------
drivers/video/fbdev/s3fb.c | 35 ++++-------------------
drivers/video/fbdev/vt8623fb.c | 31 ++++-----------------
include/asm-generic/pci_iomap.h | 14 ++++++++++
lib/pci_iomap.c | 61 +++++++++++++++++++++++++++++++++++++++++
5 files changed, 92 insertions(+), 85 deletions(-)
--
2.3.2.209.gd67f9d5.dirty
From: "Luis R. Rodriguez" <[email protected]>
This allows drivers to take advantage of write-combining
when possible. The PCI specification does not allow for us
to automatically identify a memory region which needs
write-combining so drivers have to identify these areas
on their own. There is IORESOURCE_PREFETCH but as clarified
by Michael and confirmed later by Bjorn, PCI prefetch bit
merely means bridges can combine writes and prefetch reads.
Prefetch does not affect ordering rules and does not allow
writes to be collapsed [0]. WC is stronger, it allows collapsing
and changes ordering rules. WC can also hurt latency as small
writes are buffered. Because of all this drivers needs to
know what they are doing, we can't set a write-combining
preference flag in the pci core automatically for drivers.
Lastly although there is also arch_phys_wc_add() this makes
use of architecture specific write-combining *hacks* and
the only one currently defined and used is MTRR for x86.
MTRRs are legacy, limited in number, have restrictive size
constraints, and are known to interact pooly with the BIOS.
MTRRs should only really be considered on old video framebuffer
drivers. If we made ioremap_wc() and similar calls start
automatically adding MTRRs, then performance will vary wildly
with the order of driver loading because we'll run out of MTRRs
part-way through bootup.
There are a few motivations for phasing out of MTRR and
helping driver change over to use write-combining with PAT:
a) Take advantage of PAT when available
b) Help bury MTRR code away, MTRR is architecture specific and on
x86 its replaced by PAT
c) Help with the goal of eventually using _PAGE_CACHE_UC over
_PAGE_CACHE_UC_MINUS on x86 on ioremap_nocache() (see commit
de33c442e titled "x86 PAT: fix performance drop for glx,
use UC minus for ioremap(), ioremap_nocache() and
pci_mmap_page_range()")
[0] https://lkml.org/lkml/2015/4/21/714
Cc: Toshi Kani <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Suresh Siddha <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Juergen Gross <[email protected]>
Cc: Daniel Vetter <[email protected]>
Cc: Dave Airlie <[email protected]>
Cc: Bjorn Helgaas <[email protected]>
Cc: Antonino Daplas <[email protected]>
Cc: Jean-Christophe Plagniol-Villard <[email protected]>
Cc: Tomi Valkeinen <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Cc: Michael S. Tsirkin <[email protected]>
Cc: [email protected]
Cc: Stefan Bader <[email protected]>
Cc: Ville Syrjälä <[email protected]>
Cc: Mel Gorman <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Davidlohr Bueso <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: Roger Pau Monné <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Acked-by: Bjorn Helgaas <[email protected]>
Signed-off-by: Luis R. Rodriguez <[email protected]>
---
include/asm-generic/pci_iomap.h | 14 ++++++++++
lib/pci_iomap.c | 61 +++++++++++++++++++++++++++++++++++++++++
2 files changed, 75 insertions(+)
diff --git a/include/asm-generic/pci_iomap.h b/include/asm-generic/pci_iomap.h
index 7389c87..b1e17fc 100644
--- a/include/asm-generic/pci_iomap.h
+++ b/include/asm-generic/pci_iomap.h
@@ -15,9 +15,13 @@ struct pci_dev;
#ifdef CONFIG_PCI
/* Create a virtual mapping cookie for a PCI BAR (memory or IO) */
extern void __iomem *pci_iomap(struct pci_dev *dev, int bar, unsigned long max);
+extern void __iomem *pci_iomap_wc(struct pci_dev *dev, int bar, unsigned long max);
extern void __iomem *pci_iomap_range(struct pci_dev *dev, int bar,
unsigned long offset,
unsigned long maxlen);
+extern void __iomem *pci_iomap_wc_range(struct pci_dev *dev, int bar,
+ unsigned long offset,
+ unsigned long maxlen);
/* Create a virtual mapping cookie for a port on a given PCI device.
* Do not call this directly, it exists to make it easier for architectures
* to override */
@@ -34,12 +38,22 @@ static inline void __iomem *pci_iomap(struct pci_dev *dev, int bar, unsigned lon
return NULL;
}
+static inline void __iomem *pci_iomap_wc(struct pci_dev *dev, int bar, unsigned long max)
+{
+ return NULL;
+}
static inline void __iomem *pci_iomap_range(struct pci_dev *dev, int bar,
unsigned long offset,
unsigned long maxlen)
{
return NULL;
}
+static inline void __iomem *pci_iomap_wc_range(struct pci_dev *dev, int bar,
+ unsigned long offset,
+ unsigned long maxlen)
+{
+ return NULL;
+}
#endif
#endif /* __ASM_GENERIC_IO_H */
diff --git a/lib/pci_iomap.c b/lib/pci_iomap.c
index bcce5f1..9604dcb 100644
--- a/lib/pci_iomap.c
+++ b/lib/pci_iomap.c
@@ -52,6 +52,46 @@ void __iomem *pci_iomap_range(struct pci_dev *dev,
EXPORT_SYMBOL(pci_iomap_range);
/**
+ * pci_iomap_wc_range - create a virtual WC mapping cookie for a PCI BAR
+ * @dev: PCI device that owns the BAR
+ * @bar: BAR number
+ * @offset: map memory at the given offset in BAR
+ * @maxlen: max length of the memory to map
+ *
+ * Using this function you will get a __iomem address to your device BAR.
+ * You can access it using ioread*() and iowrite*(). These functions hide
+ * the details if this is a MMIO or PIO address space and will just do what
+ * you expect from them in the correct way. When possible write combining
+ * is used.
+ *
+ * @maxlen specifies the maximum length to map. If you want to get access to
+ * the complete BAR from offset to the end, pass %0 here.
+ * */
+void __iomem *pci_iomap_wc_range(struct pci_dev *dev,
+ int bar,
+ unsigned long offset,
+ unsigned long maxlen)
+{
+ resource_size_t start = pci_resource_start(dev, bar);
+ resource_size_t len = pci_resource_len(dev, bar);
+ unsigned long flags = pci_resource_flags(dev, bar);
+
+ if (len <= offset || !start)
+ return NULL;
+ len -= offset;
+ start += offset;
+ if (maxlen && len > maxlen)
+ len = maxlen;
+ if (flags & IORESOURCE_IO)
+ return NULL;
+ if (flags & IORESOURCE_MEM)
+ return ioremap_wc(start, len);
+ /* What? */
+ return NULL;
+}
+EXPORT_SYMBOL_GPL(pci_iomap_wc_range);
+
+/**
* pci_iomap - create a virtual mapping cookie for a PCI BAR
* @dev: PCI device that owns the BAR
* @bar: BAR number
@@ -70,4 +110,25 @@ void __iomem *pci_iomap(struct pci_dev *dev, int bar, unsigned long maxlen)
return pci_iomap_range(dev, bar, 0, maxlen);
}
EXPORT_SYMBOL(pci_iomap);
+
+/**
+ * pci_iomap_wc - create a virtual WC mapping cookie for a PCI BAR
+ * @dev: PCI device that owns the BAR
+ * @bar: BAR number
+ * @maxlen: length of the memory to map
+ *
+ * Using this function you will get a __iomem address to your device BAR.
+ * You can access it using ioread*() and iowrite*(). These functions hide
+ * the details if this is a MMIO or PIO address space and will just do what
+ * you expect from them in the correct way. When possible write combining
+ * is used.
+ *
+ * @maxlen specifies the maximum length to map. If you want to get access to
+ * the complete BAR without checking for its length first, pass %0 here.
+ * */
+void __iomem *pci_iomap_wc(struct pci_dev *dev, int bar, unsigned long maxlen)
+{
+ return pci_iomap_wc_range(dev, bar, 0, maxlen);
+}
+EXPORT_SYMBOL_GPL(pci_iomap_wc);
#endif /* CONFIG_PCI */
--
2.3.2.209.gd67f9d5.dirty
From: "Luis R. Rodriguez" <[email protected]>
Convert the driver from using the x86 specific MTRR code to
the architecture agnostic arch_phys_wc_add(). arch_phys_wc_add()
will avoid MTRR if write-combining is available, in order to
take advantage of that also ensure the ioremap'd area is requested
as write-combining.
There are a few motivations for this:
a) Take advantage of PAT when available
b) Help bury MTRR code away, MTRR is architecture specific and on
x86 its replaced by PAT
c) Help with the goal of eventually using _PAGE_CACHE_UC over
_PAGE_CACHE_UC_MINUS on x86 on ioremap_nocache() (see commit
de33c442e titled "x86 PAT: fix performance drop for glx,
use UC minus for ioremap(), ioremap_nocache() and
pci_mmap_page_range()")
The conversion done is expressed by the following Coccinelle
SmPL patch, it additionally required manual intervention to
address all the #ifdery and removal of redundant things which
arch_phys_wc_add() already addresses such as verbose message
about when MTRR fails and doing nothing when we didn't get
an MTRR.
@ mtrr_found @
expression index, base, size;
@@
-index = mtrr_add(base, size, MTRR_TYPE_WRCOMB, 1);
+index = arch_phys_wc_add(base, size);
@ mtrr_rm depends on mtrr_found @
expression mtrr_found.index, mtrr_found.base, mtrr_found.size;
@@
-mtrr_del(index, base, size);
+arch_phys_wc_del(index);
@ mtrr_rm_zero_arg depends on mtrr_found @
expression mtrr_found.index;
@@
-mtrr_del(index, 0, 0);
+arch_phys_wc_del(index);
@ mtrr_rm_fb_info depends on mtrr_found @
struct fb_info *info;
expression mtrr_found.index;
@@
-mtrr_del(index, info->fix.smem_start, info->fix.smem_len);
+arch_phys_wc_del(index);
@ ioremap_replace_nocache depends on mtrr_found @
struct fb_info *info;
expression base, size;
@@
-info->screen_base = ioremap_nocache(base, size);
+info->screen_base = ioremap_wc(base, size);
@ ioremap_replace_default depends on mtrr_found @
struct fb_info *info;
expression base, size;
@@
-info->screen_base = ioremap(base, size);
+info->screen_base = ioremap_wc(base, size);
Generated-by: Coccinelle SmPL
Cc: Laurent Pinchart <[email protected]>
Cc: Geert Uytterhoeven <[email protected]>
Cc: "Lad, Prabhakar" <[email protected]>
Cc: Suresh Siddha <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Juergen Gross <[email protected]>
Cc: Daniel Vetter <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Dave Airlie <[email protected]>
Cc: Antonino Daplas <[email protected]>
Cc: Jean-Christophe Plagniol-Villard <[email protected]>
Cc: Tomi Valkeinen <[email protected]>
Cc: [email protected]
Cc: [email protected]
Acked-by: Tomi Valkeinen <[email protected]>
Signed-off-by: Luis R. Rodriguez <[email protected]>
---
drivers/video/fbdev/arkfb.c | 36 +++++-------------------------------
1 file changed, 5 insertions(+), 31 deletions(-)
diff --git a/drivers/video/fbdev/arkfb.c b/drivers/video/fbdev/arkfb.c
index b305a1e..6a317de 100644
--- a/drivers/video/fbdev/arkfb.c
+++ b/drivers/video/fbdev/arkfb.c
@@ -26,13 +26,9 @@
#include <linux/console.h> /* Why should fb driver call console functions? because console_lock() */
#include <video/vga.h>
-#ifdef CONFIG_MTRR
-#include <asm/mtrr.h>
-#endif
-
struct arkfb_info {
int mclk_freq;
- int mtrr_reg;
+ int wc_cookie;
struct dac_info *dac;
struct vgastate state;
@@ -102,10 +98,6 @@ static const struct svga_timing_regs ark_timing_regs = {
static char *mode_option = "640x480-8@60";
-#ifdef CONFIG_MTRR
-static int mtrr = 1;
-#endif
-
MODULE_AUTHOR("(c) 2007 Ondrej Zajicek <[email protected]>");
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("fbdev driver for ARK 2000PV");
@@ -115,11 +107,6 @@ MODULE_PARM_DESC(mode_option, "Default video mode ('640x480-8@60', etc)");
module_param_named(mode, mode_option, charp, 0444);
MODULE_PARM_DESC(mode, "Default video mode ('640x480-8@60', etc) (deprecated)");
-#ifdef CONFIG_MTRR
-module_param(mtrr, int, 0444);
-MODULE_PARM_DESC(mtrr, "Enable write-combining with MTRR (1=enable, 0=disable, default=1)");
-#endif
-
static int threshold = 4;
module_param(threshold, int, 0644);
@@ -1002,7 +989,7 @@ static int ark_pci_probe(struct pci_dev *dev, const struct pci_device_id *id)
info->fix.smem_len = pci_resource_len(dev, 0);
/* Map physical IO memory address into kernel space */
- info->screen_base = pci_iomap(dev, 0, 0);
+ info->screen_base = pci_iomap_wc(dev, 0, 0);
if (! info->screen_base) {
rc = -ENOMEM;
dev_err(info->device, "iomap for framebuffer failed\n");
@@ -1057,14 +1044,8 @@ static int ark_pci_probe(struct pci_dev *dev, const struct pci_device_id *id)
/* Record a reference to the driver data */
pci_set_drvdata(dev, info);
-
-#ifdef CONFIG_MTRR
- if (mtrr) {
- par->mtrr_reg = -1;
- par->mtrr_reg = mtrr_add(info->fix.smem_start, info->fix.smem_len, MTRR_TYPE_WRCOMB, 1);
- }
-#endif
-
+ par->wc_cookie = arch_phys_wc_add(info->fix.smem_start,
+ info->fix.smem_len);
return 0;
/* Error handling */
@@ -1092,14 +1073,7 @@ static void ark_pci_remove(struct pci_dev *dev)
if (info) {
struct arkfb_info *par = info->par;
-
-#ifdef CONFIG_MTRR
- if (par->mtrr_reg >= 0) {
- mtrr_del(par->mtrr_reg, 0, 0);
- par->mtrr_reg = -1;
- }
-#endif
-
+ arch_phys_wc_del(par->wc_cookie);
dac_release(par->dac);
unregister_framebuffer(info);
fb_dealloc_cmap(&info->cmap);
--
2.3.2.209.gd67f9d5.dirty
From: "Luis R. Rodriguez" <[email protected]>
This driver uses the same area for MTRR as for the ioremap().
Convert the driver from using the x86 specific MTRR code to
the architecture agnostic arch_phys_wc_add(). arch_phys_wc_add()
will avoid MTRR if write-combining is available, in order to
take advantage of that also ensure the ioremap'd area is requested
as write-combining.
There are a few motivations for this:
a) Take advantage of PAT when available
b) Help bury MTRR code away, MTRR is architecture specific and on
x86 its replaced by PAT
c) Help with the goal of eventually using _PAGE_CACHE_UC over
_PAGE_CACHE_UC_MINUS on x86 on ioremap_nocache() (see commit
de33c442e titled "x86 PAT: fix performance drop for glx,
use UC minus for ioremap(), ioremap_nocache() and
pci_mmap_page_range()")
The conversion done is expressed by the following Coccinelle
SmPL patch, it additionally required manual intervention to
address all the #ifdery and removal of redundant things which
arch_phys_wc_add() already addresses such as verbose message
about when MTRR fails and doing nothing when we didn't get
an MTRR.
@ mtrr_found @
expression index, base, size;
@@
-index = mtrr_add(base, size, MTRR_TYPE_WRCOMB, 1);
+index = arch_phys_wc_add(base, size);
@ mtrr_rm depends on mtrr_found @
expression mtrr_found.index, mtrr_found.base, mtrr_found.size;
@@
-mtrr_del(index, base, size);
+arch_phys_wc_del(index);
@ mtrr_rm_zero_arg depends on mtrr_found @
expression mtrr_found.index;
@@
-mtrr_del(index, 0, 0);
+arch_phys_wc_del(index);
@ mtrr_rm_fb_info depends on mtrr_found @
struct fb_info *info;
expression mtrr_found.index;
@@
-mtrr_del(index, info->fix.smem_start, info->fix.smem_len);
+arch_phys_wc_del(index);
@ ioremap_replace_nocache depends on mtrr_found @
struct fb_info *info;
expression base, size;
@@
-info->screen_base = ioremap_nocache(base, size);
+info->screen_base = ioremap_wc(base, size);
@ ioremap_replace_default depends on mtrr_found @
struct fb_info *info;
expression base, size;
@@
-info->screen_base = ioremap(base, size);
+info->screen_base = ioremap_wc(base, size);
Generated-by: Coccinelle SmPL
Cc: Jean-Christophe Plagniol-Villard <[email protected]>
Cc: Tomi Valkeinen <[email protected]>
Cc: Jingoo Han <[email protected]>
Cc: Geert Uytterhoeven <[email protected]>
Cc: Daniel Vetter <[email protected]>
Cc: "Lad, Prabhakar" <[email protected]>
Cc: Rickard Strandqvist <[email protected]>
Cc: Suresh Siddha <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Juergen Gross <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Dave Airlie <[email protected]>
Cc: Antonino Daplas <[email protected]>
Cc: [email protected]
Cc: [email protected]
Acked-by: Tomi Valkeinen <[email protected]>
Signed-off-by: Luis R. Rodriguez <[email protected]>
---
drivers/video/fbdev/s3fb.c | 35 ++++++-----------------------------
1 file changed, 6 insertions(+), 29 deletions(-)
diff --git a/drivers/video/fbdev/s3fb.c b/drivers/video/fbdev/s3fb.c
index f0ae61a..13b1090 100644
--- a/drivers/video/fbdev/s3fb.c
+++ b/drivers/video/fbdev/s3fb.c
@@ -28,13 +28,9 @@
#include <linux/i2c.h>
#include <linux/i2c-algo-bit.h>
-#ifdef CONFIG_MTRR
-#include <asm/mtrr.h>
-#endif
-
struct s3fb_info {
int chip, rev, mclk_freq;
- int mtrr_reg;
+ int wc_cookie;
struct vgastate state;
struct mutex open_lock;
unsigned int ref_count;
@@ -154,11 +150,7 @@ static const struct svga_timing_regs s3_timing_regs = {
static char *mode_option;
-
-#ifdef CONFIG_MTRR
static int mtrr = 1;
-#endif
-
static int fasttext = 1;
@@ -170,11 +162,8 @@ module_param(mode_option, charp, 0444);
MODULE_PARM_DESC(mode_option, "Default video mode ('640x480-8@60', etc)");
module_param_named(mode, mode_option, charp, 0444);
MODULE_PARM_DESC(mode, "Default video mode ('640x480-8@60', etc) (deprecated)");
-
-#ifdef CONFIG_MTRR
module_param(mtrr, int, 0444);
MODULE_PARM_DESC(mtrr, "Enable write-combining with MTRR (1=enable, 0=disable, default=1)");
-#endif
module_param(fasttext, int, 0644);
MODULE_PARM_DESC(fasttext, "Enable S3 fast text mode (1=enable, 0=disable, default=1)");
@@ -1168,7 +1157,7 @@ static int s3_pci_probe(struct pci_dev *dev, const struct pci_device_id *id)
info->fix.smem_len = pci_resource_len(dev, 0);
/* Map physical IO memory address into kernel space */
- info->screen_base = pci_iomap(dev, 0, 0);
+ info->screen_base = pci_iomap_wc(dev, 0, 0);
if (! info->screen_base) {
rc = -ENOMEM;
dev_err(info->device, "iomap for framebuffer failed\n");
@@ -1365,12 +1354,9 @@ static int s3_pci_probe(struct pci_dev *dev, const struct pci_device_id *id)
/* Record a reference to the driver data */
pci_set_drvdata(dev, info);
-#ifdef CONFIG_MTRR
- if (mtrr) {
- par->mtrr_reg = -1;
- par->mtrr_reg = mtrr_add(info->fix.smem_start, info->fix.smem_len, MTRR_TYPE_WRCOMB, 1);
- }
-#endif
+ if (mtrr)
+ par->wc_cookie = arch_phys_wc_add(info->fix.smem_start,
+ info->fix.smem_len);
return 0;
@@ -1405,14 +1391,7 @@ static void s3_pci_remove(struct pci_dev *dev)
if (info) {
par = info->par;
-
-#ifdef CONFIG_MTRR
- if (par->mtrr_reg >= 0) {
- mtrr_del(par->mtrr_reg, 0, 0);
- par->mtrr_reg = -1;
- }
-#endif
-
+ arch_phys_wc_del(par->wc_cookie);
unregister_framebuffer(info);
fb_dealloc_cmap(&info->cmap);
@@ -1551,10 +1530,8 @@ static int __init s3fb_setup(char *options)
if (!*opt)
continue;
-#ifdef CONFIG_MTRR
else if (!strncmp(opt, "mtrr:", 5))
mtrr = simple_strtoul(opt + 5, NULL, 0);
-#endif
else if (!strncmp(opt, "fasttext:", 9))
fasttext = simple_strtoul(opt + 9, NULL, 0);
else
--
2.3.2.209.gd67f9d5.dirty
From: "Luis R. Rodriguez" <[email protected]>
This driver uses the same area for MTRR as for the ioremap().
Convert the driver from using the x86 specific MTRR code to
the architecture agnostic arch_phys_wc_add(). arch_phys_wc_add()
will avoid MTRR if write-combining is available, in order to
take advantage of that also ensure the ioremap'd area is requested
as write-combining.
There are a few motivations for this:
a) Take advantage of PAT when available
b) Help bury MTRR code away, MTRR is architecture specific and on
x86 its replaced by PAT
c) Help with the goal of eventually using _PAGE_CACHE_UC over
_PAGE_CACHE_UC_MINUS on x86 on ioremap_nocache() (see commit
de33c442e titled "x86 PAT: fix performance drop for glx,
use UC minus for ioremap(), ioremap_nocache() and
pci_mmap_page_range()")
The conversion done is expressed by the following Coccinelle
SmPL patch, it additionally required manual intervention to
address all the #ifdery and removal of redundant things which
arch_phys_wc_add() already addresses such as verbose message
about when MTRR fails and doing nothing when we didn't get
an MTRR.
@ mtrr_found @
expression index, base, size;
@@
-index = mtrr_add(base, size, MTRR_TYPE_WRCOMB, 1);
+index = arch_phys_wc_add(base, size);
@ mtrr_rm depends on mtrr_found @
expression mtrr_found.index, mtrr_found.base, mtrr_found.size;
@@
-mtrr_del(index, base, size);
+arch_phys_wc_del(index);
@ mtrr_rm_zero_arg depends on mtrr_found @
expression mtrr_found.index;
@@
-mtrr_del(index, 0, 0);
+arch_phys_wc_del(index);
@ mtrr_rm_fb_info depends on mtrr_found @
struct fb_info *info;
expression mtrr_found.index;
@@
-mtrr_del(index, info->fix.smem_start, info->fix.smem_len);
+arch_phys_wc_del(index);
@ ioremap_replace_nocache depends on mtrr_found @
struct fb_info *info;
expression base, size;
@@
-info->screen_base = ioremap_nocache(base, size);
+info->screen_base = ioremap_wc(base, size);
@ ioremap_replace_default depends on mtrr_found @
struct fb_info *info;
expression base, size;
@@
-info->screen_base = ioremap(base, size);
+info->screen_base = ioremap_wc(base, size);
Generated-by: Coccinelle SmPL
Cc: Rob Clark <[email protected]>
Cc: Laurent Pinchart <[email protected]>
Cc: Jingoo Han <[email protected]>
Cc: "Lad, Prabhakar" <[email protected]>
Cc: Suresh Siddha <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Juergen Gross <[email protected]>
Cc: Daniel Vetter <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Dave Airlie <[email protected]>
Cc: Antonino Daplas <[email protected]>
Cc: Jean-Christophe Plagniol-Villard <[email protected]>
Cc: Tomi Valkeinen <[email protected]>
Cc: [email protected]
Cc: [email protected]
Acked-by: Tomi Valkeinen <[email protected]>
Signed-off-by: Luis R. Rodriguez <[email protected]>
---
drivers/video/fbdev/vt8623fb.c | 31 ++++++-------------------------
1 file changed, 6 insertions(+), 25 deletions(-)
diff --git a/drivers/video/fbdev/vt8623fb.c b/drivers/video/fbdev/vt8623fb.c
index ea7f056..60f24828 100644
--- a/drivers/video/fbdev/vt8623fb.c
+++ b/drivers/video/fbdev/vt8623fb.c
@@ -26,13 +26,9 @@
#include <linux/console.h> /* Why should fb driver call console functions? because console_lock() */
#include <video/vga.h>
-#ifdef CONFIG_MTRR
-#include <asm/mtrr.h>
-#endif
-
struct vt8623fb_info {
char __iomem *mmio_base;
- int mtrr_reg;
+ int wc_cookie;
struct vgastate state;
struct mutex open_lock;
unsigned int ref_count;
@@ -99,10 +95,7 @@ static struct svga_timing_regs vt8623_timing_regs = {
/* Module parameters */
static char *mode_option = "640x480-8@60";
-
-#ifdef CONFIG_MTRR
static int mtrr = 1;
-#endif
MODULE_AUTHOR("(c) 2006 Ondrej Zajicek <[email protected]>");
MODULE_LICENSE("GPL");
@@ -112,11 +105,8 @@ module_param(mode_option, charp, 0644);
MODULE_PARM_DESC(mode_option, "Default video mode ('640x480-8@60', etc)");
module_param_named(mode, mode_option, charp, 0);
MODULE_PARM_DESC(mode, "Default video mode e.g. '648x480-8@60' (deprecated)");
-
-#ifdef CONFIG_MTRR
module_param(mtrr, int, 0444);
MODULE_PARM_DESC(mtrr, "Enable write-combining with MTRR (1=enable, 0=disable, default=1)");
-#endif
/* ------------------------------------------------------------------------- */
@@ -710,7 +700,7 @@ static int vt8623_pci_probe(struct pci_dev *dev, const struct pci_device_id *id)
info->fix.mmio_len = pci_resource_len(dev, 1);
/* Map physical IO memory address into kernel space */
- info->screen_base = pci_iomap(dev, 0, 0);
+ info->screen_base = pci_iomap_wc(dev, 0, 0);
if (! info->screen_base) {
rc = -ENOMEM;
dev_err(info->device, "iomap for framebuffer failed\n");
@@ -781,12 +771,9 @@ static int vt8623_pci_probe(struct pci_dev *dev, const struct pci_device_id *id)
/* Record a reference to the driver data */
pci_set_drvdata(dev, info);
-#ifdef CONFIG_MTRR
- if (mtrr) {
- par->mtrr_reg = -1;
- par->mtrr_reg = mtrr_add(info->fix.smem_start, info->fix.smem_len, MTRR_TYPE_WRCOMB, 1);
- }
-#endif
+ if (mtrr)
+ par->wc_cookie = arch_phys_wc_add(info->fix.smem_start,
+ info->fix.smem_len);
return 0;
@@ -816,13 +803,7 @@ static void vt8623_pci_remove(struct pci_dev *dev)
if (info) {
struct vt8623fb_info *par = info->par;
-#ifdef CONFIG_MTRR
- if (par->mtrr_reg >= 0) {
- mtrr_del(par->mtrr_reg, 0, 0);
- par->mtrr_reg = -1;
- }
-#endif
-
+ arch_phys_wc_del(par->wc_cookie);
unregister_framebuffer(info);
fb_dealloc_cmap(&info->cmap);
--
2.3.2.209.gd67f9d5.dirty
On Wed, May 20, 2015 at 04:08:10PM -0700, Luis R. Rodriguez wrote:
> ...
> --- a/lib/pci_iomap.c
> +++ b/lib/pci_iomap.c
> @@ -52,6 +52,46 @@ void __iomem *pci_iomap_range(struct pci_dev *dev,
> EXPORT_SYMBOL(pci_iomap_range);
>
> /**
> + * pci_iomap_wc_range - create a virtual WC mapping cookie for a PCI BAR
> + * @dev: PCI device that owns the BAR
> + * @bar: BAR number
> + * @offset: map memory at the given offset in BAR
> + * @maxlen: max length of the memory to map
> + *
> + * Using this function you will get a __iomem address to your device BAR.
> + * You can access it using ioread*() and iowrite*(). These functions hide
> + * the details if this is a MMIO or PIO address space and will just do what
> + * you expect from them in the correct way. When possible write combining
> + * is used.
> + *
> + * @maxlen specifies the maximum length to map. If you want to get access to
> + * the complete BAR from offset to the end, pass %0 here.
> + * */
> +void __iomem *pci_iomap_wc_range(struct pci_dev *dev,
> + int bar,
> + unsigned long offset,
> + unsigned long maxlen)
> +{
> + resource_size_t start = pci_resource_start(dev, bar);
> + resource_size_t len = pci_resource_len(dev, bar);
> + unsigned long flags = pci_resource_flags(dev, bar);
> +
> + if (len <= offset || !start)
> + return NULL;
> + len -= offset;
> + start += offset;
> + if (maxlen && len > maxlen)
> + len = maxlen;
> + if (flags & IORESOURCE_IO)
> + return NULL;
> + if (flags & IORESOURCE_MEM)
> + return ioremap_wc(start, len);
> + /* What? */
> + return NULL;
> +}
> +EXPORT_SYMBOL_GPL(pci_iomap_wc_range);
> +
> +/**
> * pci_iomap - create a virtual mapping cookie for a PCI BAR
> * @dev: PCI device that owns the BAR
> * @bar: BAR number
> @@ -70,4 +110,25 @@ void __iomem *pci_iomap(struct pci_dev *dev, int bar, unsigned long maxlen)
> return pci_iomap_range(dev, bar, 0, maxlen);
> }
> EXPORT_SYMBOL(pci_iomap);
> +
> +/**
> + * pci_iomap_wc - create a virtual WC mapping cookie for a PCI BAR
> + * @dev: PCI device that owns the BAR
> + * @bar: BAR number
> + * @maxlen: length of the memory to map
> + *
> + * Using this function you will get a __iomem address to your device BAR.
> + * You can access it using ioread*() and iowrite*(). These functions hide
> + * the details if this is a MMIO or PIO address space and will just do what
> + * you expect from them in the correct way. When possible write combining
> + * is used.
> + *
> + * @maxlen specifies the maximum length to map. If you want to get access to
> + * the complete BAR without checking for its length first, pass %0 here.
> + * */
> +void __iomem *pci_iomap_wc(struct pci_dev *dev, int bar, unsigned long maxlen)
> +{
> + return pci_iomap_wc_range(dev, bar, 0, maxlen);
> +}
> +EXPORT_SYMBOL_GPL(pci_iomap_wc);
Huh. So you let me talk about marking the unused pcim_iomap_wc()
EXPORT_SYMBOL_GPL(), but didn't remind me that you also proposed to mark
the symbol you really care about, the one you already have a use for, as
EXPORT_SYMBOL_GPL(). Sigh.
In my opinion, if we're going to use EXPORT_SYMBOL_GPL() at all, we should
use it consistently and based on technical considerations. I base this on
statements like the following:
- "[EXPORT_SYMBOL_GPL()] implies that the function is considered an
internal implementation issue, and not really an interface." [Rusty
Russell, 1]
- "... using the xxx_GPL() version to show that it's an internal
interface ..." [Linus Torvalds, 2]
- "Anything exported via EXPORT_SYMBOL_GPL() is considered by the author
to be so fundamental to the kernel that using it would be impossible
without creating a derivative work." [Matthew Garrett, 3]
- "Linus's initial point for [_GPL symbols] has been so diluted by random
lobby groups asking for every symbol to be _GPL that they are becoming
effectively pointless now." [Dave Airlie, 4]
Existing interfaces like these are exported with EXPORT_SYMBOL():
ioremap()
ioremap_wc()
ioremap_prot()
pci_iomap()
pci_map_rom()
I would argue that pci_iomap_wc() is similar in spirit and is no more an
internal implementation issue than they are, and should be exported
similarly.
So my *advice* is to use EXPORT_SYMBOL() in this case, because that's a
choice you can defend on technical grounds. I think it's hard to argue
that pci_iomap_wc() is so fundamental or unique to Linux that a caller
would automatically be a derivative work.
Will I still merge it as EXPORT_SYMBOL_GPL()? Maybe. I don't feel *good*
about it because the only explanation I can give is "the author wanted it
that way," and that's unsatisfying. But I did already ack it (before I
noticed the _GPL() issue), and I won't try to retract that and prevent
somebody else from merging it. And maybe your proposal to clarify the
kernel-hacking.tmpl language will convince me.
Bjorn
[1] http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=b6c17ea4eff3
[2] http://lkml.kernel.org/r/[email protected]
[3] http://mjg59.dreamwidth.org/31357.html
[4] http://lkml.kernel.org/r/CAPM=9tzsT+nah2P-qZ8iKW=aTZJzYgm18mMWyy2-RVkoOSwyjg@mail.gmail.com
On Wed, May 20, 2015 at 04:08:10PM -0700, Luis R. Rodriguez wrote:
> From: "Luis R. Rodriguez" <[email protected]>
>
> This allows drivers to take advantage of write-combining
> when possible. The PCI specification does not allow for us
> to automatically identify a memory region which needs
> write-combining so drivers have to identify these areas
> on their own. There is IORESOURCE_PREFETCH but as clarified
> by Michael and confirmed later by Bjorn, PCI prefetch bit
> merely means bridges can combine writes and prefetch reads.
> Prefetch does not affect ordering rules and does not allow
> writes to be collapsed [0]. WC is stronger, it allows collapsing
> and changes ordering rules. WC can also hurt latency as small
> writes are buffered. Because of all this drivers needs to
> know what they are doing, we can't set a write-combining
> preference flag in the pci core automatically for drivers.
>
> Lastly although there is also arch_phys_wc_add() this makes
> use of architecture specific write-combining *hacks* and
> the only one currently defined and used is MTRR for x86.
> MTRRs are legacy, limited in number, have restrictive size
> constraints, and are known to interact pooly with the BIOS.
> MTRRs should only really be considered on old video framebuffer
> drivers. If we made ioremap_wc() and similar calls start
> automatically adding MTRRs, then performance will vary wildly
> with the order of driver loading because we'll run out of MTRRs
> part-way through bootup.
>
> There are a few motivations for phasing out of MTRR and
> helping driver change over to use write-combining with PAT:
>
> a) Take advantage of PAT when available
>
> b) Help bury MTRR code away, MTRR is architecture specific and on
> x86 its replaced by PAT
>
> c) Help with the goal of eventually using _PAGE_CACHE_UC over
> _PAGE_CACHE_UC_MINUS on x86 on ioremap_nocache() (see commit
> de33c442e titled "x86 PAT: fix performance drop for glx,
> use UC minus for ioremap(), ioremap_nocache() and
> pci_mmap_page_range()")
>
> [0] https://lkml.org/lkml/2015/4/21/714
I tentatively put this (and the rest of the series) on a pci/resource
branch. I'm hoping you'll propose some clarification about
EXPORT_SYMBOL_GPL().
In the meantime, I tried to make the changelog a bit more concise, as
below. Let me know if I omitted something essential. We still have URLs
for the discussion for the fine points.
commit 75387ae87b7aebc2a5b447f4d1b8b17a23c15b08
Author: Luis R. Rodriguez <[email protected]>
Date: Wed May 20 16:08:10 2015 -0700
PCI: Add pci_iomap_wc() variants
PCI BARs tell us whether prefetching is safe, but they don't say anything
about write combining (WC). WC changes ordering rules and allows writes to
be collapsed, so it's not safe in general to use it on a prefetchable
region.
Add pci_iomap_wc() and pci_iomap_wc_range() so drivers can take advantage
of write combining when they know it's safe.
On architectures that don't fully support WC, e.g., x86 without PAT,
drivers for legacy framebuffers may get some of the benefit by using
arch_phys_wc_add() in addition to pci_iomap_wc(). But arch_phys_wc_add()
is unreliable and should be avoided in general. On x86, it uses MTRRs,
which are limited in number and size, so the results will vary based on
driver loading order.
The goals of adding pci_iomap_wc() are to:
- Give drivers an architecture-independent way to use WC so they can stop
using interfaces like mtrr_add() (on x86, pci_iomap_wc() uses PAT when
available)
- Move toward using _PAGE_CACHE_MODE_UC, not _PAGE_CACHE_MODE_UC_MINUS,
on x86 on ioremap_nocache() (see de33c442ed2a ("x86 PAT: fix
performance drop for glx, use UC minus for ioremap(), ioremap_nocache()
and pci_mmap_page_range()")
[bhelgaas: changelog]
Link: http://lkml.kernel.org/r/[email protected]
Original-posting: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Luis R. Rodriguez <[email protected]>
Signed-off-by: Bjorn Helgaas <[email protected]>
On Thu, May 21, 2015 at 05:33:21PM -0500, Bjorn Helgaas wrote:
>
> I tentatively put this (and the rest of the series) on a pci/resource
> branch. I'm hoping you'll propose some clarification about
> EXPORT_SYMBOL_GPL().
EXPORT_SYMBOL_GPL() also serves to ensure only GPL modules can
only run that code. So for instance although we have "Dual BSD/GPL"
tags for modules pure "BSD" tags do not exist for module tags and
cannot run EXPORT_SYMBOL_GPL() code [0]. Also there is some folks
who do believe tha at run time all kernel modules are GPL [1] [2].
And to be precise even though the FSF may claim a list of licenses
are GPL-compatible we cannot rely on this list alone for our own
goals and if folks want to use our EXPORT_SYMBOL_GPL()s they must
discuss this on lkml [2].
In the past when I've tried to try to clarify EXPORT_SYMBOL_GPL()
requirements, implications, its been said that its best to leave
some things as-is [3] and let attorneys figure things out. In so
far as to what exactly it is and can be used for requires legal
attorney review, but the question of derivative work certainly
comes up [4]. Now folks companies seem to want to obviously use
and abuse our symbols despite of all the things above, for instance
Red Hat once tried to change an EXPORT_SYMBOL_GPL() to
EXPORT_SYMBOL() [5]. Obviously that didn't go so well, and some
folks went off on a good rant about this [6].
What developers do and accept varies, I'm not going into pointing
out specifics and I do not wnat to do homework for folks who wish
to abuse things further, but by no means should a developer be
nack'd entry to new code if their functionality is not replacing
old one [9]. In this case this is new functionality. Also in terms
of preference:
"nobody has said that symbols exported with plain EXPORT_SYMBOL() can be freely
used by proprietary code; indeed, a number of developers claim that all (or
nearly all) loadable modules are derived products of the kernel regardless of
whether they use GPL-only symbols or not" [7].
And spot on:
"In general, the kernel community has long worked to maintain a vague and scary
ambiguity around the legal status of proprietary modules while being unwilling
to attempt to ban such modules outright." [7].
Now, a few maintainers insist on tons of new symbols to be EXPORT_SYMBOL_GPL()
though proactively [8] [9] and the reasons vary, I just happen to also write my
code to be perfectly clear with my goals and intent and you are the first to
ask me to reconsider this, even if you do make me use EXPORT_SYMBOL() my intent
and goal does not change, as with others. No code I ever write should be used
by proprietary shit, and I hope to convince others of the importance to do this
as well.
> In the meantime, I tried to make the changelog a bit more concise, as
> below. Let me know if I omitted something essential. We still have URLs
> for the discussion for the fine points.
Looks good.
[0] https://lkml.org/lkml/2012/4/7/102
[1] https://lkml.org/lkml/2012/4/8/71
[2] https://lkml.org/lkml/2012/4/8/71
[3] https://lkml.org/lkml/2009/6/1/385
[4] https://lkml.org/lkml/2009/6/1/376
[5] https://lkml.org/lkml/2012/4/20/328
[6] https://plus.google.com/+AlanCoxLinux/posts/D2feRNc6R4d
[7] https://lwn.net/Articles/603131/
[8] https://lwn.net/Articles/603139/
[9] https://lkml.org/lkml/2015/2/26/379
Luis
On Fri, May 22, 2015 at 02:23:41AM +0200, Luis R. Rodriguez wrote:
> On Thu, May 21, 2015 at 05:33:21PM -0500, Bjorn Helgaas wrote:
> >
> > I tentatively put this (and the rest of the series) on a pci/resource
> > branch. I'm hoping you'll propose some clarification about
> > EXPORT_SYMBOL_GPL().
>
> EXPORT_SYMBOL_GPL() also serves to ensure only GPL modules can
> only run that code. So for instance although we have "Dual BSD/GPL"
> tags for modules pure "BSD" tags do not exist for module tags and
> cannot run EXPORT_SYMBOL_GPL() code [0]. Also there is some folks
> who do believe tha at run time all kernel modules are GPL [1] [2].
> And to be precise even though the FSF may claim a list of licenses
> are GPL-compatible we cannot rely on this list alone for our own
> goals and if folks want to use our EXPORT_SYMBOL_GPL()s they must
> discuss this on lkml [2].
By "propose some clarification," I meant that I hoped you would propose a
patch to Documentation/ that would give maintainers some guidance.
> ...
On Thu, May 28, 2015 at 5:36 PM, Luis R. Rodriguez
<[email protected]> wrote:
> On Wed, May 27, 2015 at 1:04 PM, Luis R. Rodriguez <[email protected]> wrote:
>> On Tue, May 26, 2015 at 12:40:08PM -0500, Bjorn Helgaas wrote:
>>> On Fri, May 22, 2015 at 02:23:41AM +0200, Luis R. Rodriguez wrote:
>>> > On Thu, May 21, 2015 at 05:33:21PM -0500, Bjorn Helgaas wrote:
>>> > >
>>> > > I tentatively put this (and the rest of the series) on a pci/resource
>>> > > branch. I'm hoping you'll propose some clarification about
>>> > > EXPORT_SYMBOL_GPL().
>>> >
>>> > EXPORT_SYMBOL_GPL() also serves to ensure only GPL modules can
>>> > only run that code. So for instance although we have "Dual BSD/GPL"
>>> > tags for modules pure "BSD" tags do not exist for module tags and
>>> > cannot run EXPORT_SYMBOL_GPL() code [0]. Also there is some folks
>>> > who do believe tha at run time all kernel modules are GPL [1] [2].
>>> > And to be precise even though the FSF may claim a list of licenses
>>> > are GPL-compatible we cannot rely on this list alone for our own
>>> > goals and if folks want to use our EXPORT_SYMBOL_GPL()s they must
>>> > discuss this on lkml [2].
>>>
>>> By "propose some clarification," I meant that I hoped you would propose a
>>> patch to Documentation/ that would give maintainers some guidance.
>>
>> I *really really* would hate to do so but only because you insist, I'll look
>> into this...
>
> OK done.
Bjorn,
This is now on Jonathan Corbet's tree and visible on linux-next:
https://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git/commit/?id=582ed8d51e2b6cb8a168c94852bca482685c2509
> Please let me know if there is anything else I can do to
> help.
Please let me know.
> Also as per review with Tomi, the framebuffer maintainer, he
> would prefer for only the required symbols to go through your tree.
> We'd then wait for the next merge window for them to perculate to
> Linus' tree and once there I'd send him a pull request for the
> framebuffer device driver changes alone. So this does mean we'll have
> no users of the symbols for a full release, but again, this is as per
> Tomi's preference. This strategy is also the preference then for the
> pci_iomap_wc() series as well. With that in mind, perhaps the lib
> patch can go in as we'd have no users but we do have a few future
> possible expected users.
I repoked Tomi about this topic with a new context provided, my
expressed hope was to just merge the fbvdev dependent changes for both
series (now both Acked by Tomi) through your tree.
Luis
On Tue, Jun 16, 2015 at 2:16 PM, Luis R. Rodriguez
<[email protected]> wrote:
> On Thu, May 28, 2015 at 5:36 PM, Luis R. Rodriguez
> <[email protected]> wrote:
>> On Wed, May 27, 2015 at 1:04 PM, Luis R. Rodriguez <[email protected]> wrote:
>>> On Tue, May 26, 2015 at 12:40:08PM -0500, Bjorn Helgaas wrote:
>>>> On Fri, May 22, 2015 at 02:23:41AM +0200, Luis R. Rodriguez wrote:
>>>> > On Thu, May 21, 2015 at 05:33:21PM -0500, Bjorn Helgaas wrote:
>>>> > >
>>>> > > I tentatively put this (and the rest of the series) on a pci/resource
>>>> > > branch. I'm hoping you'll propose some clarification about
>>>> > > EXPORT_SYMBOL_GPL().
>>>> >
>>>> > EXPORT_SYMBOL_GPL() also serves to ensure only GPL modules can
>>>> > only run that code. So for instance although we have "Dual BSD/GPL"
>>>> > tags for modules pure "BSD" tags do not exist for module tags and
>>>> > cannot run EXPORT_SYMBOL_GPL() code [0]. Also there is some folks
>>>> > who do believe tha at run time all kernel modules are GPL [1] [2].
>>>> > And to be precise even though the FSF may claim a list of licenses
>>>> > are GPL-compatible we cannot rely on this list alone for our own
>>>> > goals and if folks want to use our EXPORT_SYMBOL_GPL()s they must
>>>> > discuss this on lkml [2].
>>>>
>>>> By "propose some clarification," I meant that I hoped you would propose a
>>>> patch to Documentation/ that would give maintainers some guidance.
>>>
>>> I *really really* would hate to do so but only because you insist, I'll look
>>> into this...
>>
>> OK done.
>
> Bjorn,
>
> This is now on Jonathan Corbet's tree and visible on linux-next:
>
> https://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git/commit/?id=582ed8d51e2b6cb8a168c94852bca482685c2509
Sorry, I'm just not comfortable with using EXPORT_SYMBOL_GPL() this
way. I'm happy to use it when it has a technical justification, e.g.,
for internal interfaces where users of the interface are clearly
derived works. But pci_iomap_wc() is not in that category, and I
think it should be symmetric with similar interfaces like pci_iomap()
and ioremap_wc().
I don't want to use EXPORT_SYMBOL_GPL() for a random collection of
things depending on the whim of the author. That makes for a messy
environment to work in, and it's messy enough already. If we wanted
to remove the EXPORT_SYMBOL/EXPORT_SYMBOL_GPL distinction completely,
that'd be fine with me, too. But as long as we keep it, I think it
should mean something more than the preference of the author.
I know I did already ack this, and I even said I would merge it, but a
month of thinking about this hasn't made me more comfortable with it,
so I've changed my mind. I said before that I wouldn't try to stop
you if you want to merge it some other way, but I don't want to ack
it, and I don't want to merge it via my tree.
Bjorn
On Tue, Jun 16, 2015 at 3:20 PM, Bjorn Helgaas <[email protected]> wrote:
> On Tue, Jun 16, 2015 at 2:16 PM, Luis R. Rodriguez
> <[email protected]> wrote:
>> On Thu, May 28, 2015 at 5:36 PM, Luis R. Rodriguez
>> <[email protected]> wrote:
>>> On Wed, May 27, 2015 at 1:04 PM, Luis R. Rodriguez <[email protected]> wrote:
>>>> On Tue, May 26, 2015 at 12:40:08PM -0500, Bjorn Helgaas wrote:
>>>>> On Fri, May 22, 2015 at 02:23:41AM +0200, Luis R. Rodriguez wrote:
>>>>> > On Thu, May 21, 2015 at 05:33:21PM -0500, Bjorn Helgaas wrote:
>>>>> > >
>>>>> > > I tentatively put this (and the rest of the series) on a pci/resource
>>>>> > > branch. I'm hoping you'll propose some clarification about
>>>>> > > EXPORT_SYMBOL_GPL().
>>>>> >
>>>>> > EXPORT_SYMBOL_GPL() also serves to ensure only GPL modules can
>>>>> > only run that code. So for instance although we have "Dual BSD/GPL"
>>>>> > tags for modules pure "BSD" tags do not exist for module tags and
>>>>> > cannot run EXPORT_SYMBOL_GPL() code [0]. Also there is some folks
>>>>> > who do believe tha at run time all kernel modules are GPL [1] [2].
>>>>> > And to be precise even though the FSF may claim a list of licenses
>>>>> > are GPL-compatible we cannot rely on this list alone for our own
>>>>> > goals and if folks want to use our EXPORT_SYMBOL_GPL()s they must
>>>>> > discuss this on lkml [2].
>>>>>
>>>>> By "propose some clarification," I meant that I hoped you would propose a
>>>>> patch to Documentation/ that would give maintainers some guidance.
>>>>
>>>> I *really really* would hate to do so but only because you insist, I'll look
>>>> into this...
>>>
>>> OK done.
>>
>> Bjorn,
>>
>> This is now on Jonathan Corbet's tree and visible on linux-next:
>>
>> https://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git/commit/?id=582ed8d51e2b6cb8a168c94852bca482685c2509
>
> Sorry, I'm just not comfortable with using EXPORT_SYMBOL_GPL() this
> way. I'm happy to use it when it has a technical justification, e.g.,
> for internal interfaces where users of the interface are clearly
> derived works.
I believe it is completely fair for some maintainers to take the
position of what the documentation used to say prior to the new
documentation patch on queue for v4.2, but note that that is an old
position and I seriously caution against it. A few reasons I caution
against it:
1) It used to be believed that EXPORT_SYMBOL_GPL() was pretty
pointless by many maintainers and developers -- in particular for all
those who have always written even EXPORT_SYMBOL() code with the same
intent as EXPORT_SYMBOL_GPL(). Experience and comments with attorneys
even on Linus' part reflects that there is a huge legal value to
EXPORT_SYMBOL_GPL() [0].
The skinny: Intent matters a lot and "circumventing a GPL-only export
requires an explicit action, making it clear that the resulting
copyright infringement was a deliberate act".
Naturally lax positions on the matter over use of EXPORT_SYMBOL_GPL()
have evolved over time then, not only about its value but also then as
a consequence about where its used in practice today by maintainers
and developers in different trees.
[0] https://lwn.net/Articles/154602/
2) The old position of use of EXPORT_SYMBOL_GPL() about the
derivatives work punts onto the maintainer the onus over the question
of derivatives work -- such question really should not be taken
lightly and this responsibility should really not fall onto the
developer, it requires attorney involvement and should not be taken
lightly by any means.
3) Most drivers are upstream these days, we want to avoid bug reports
from crappy proprietary drivers, specially as we add new features. We
don't have to be begging vendors to work upstream these days, that's
rather the norm. The landscape has changed dramatically. Even Linus
has told Nvidia to go fuck themselves lately, bravo.
> But pci_iomap_wc() is not in that category, and I
> think it should be symmetric with similar interfaces like pci_iomap()
> and ioremap_wc().
Those are two old APIs, and quite the contrary, as I noted we have a
series of new PAT APIs that old modules did not use that are now being
added and spread into the kernel onto which upstream maintainers have
been insisting on using EXPORT_SYMBOL_GPL() even though older similar
APIs only used EXPORT_SYMBOL(). As a recent example the family of APIs
set_pages_array_xx() are all EXPORT_SYMBOL() but Toshi's new
set_pages_array_wt() was asked to be changed to EXPORT_SYMBOL_GPL()
because as noted by Ingo:
--------------
By default we make new APIs EXPORT_SYMBOL_GPL():
we don't want proprietary modules mucking around with new code
PAT interfaces, we only want modules we can analyze and fix
in detail.
--------------
http://article.gmane.org/gmane.linux.kernel.mm/129104
> I don't want to use EXPORT_SYMBOL_GPL() for a random collection of
> things depending on the whim of the author.
Its not just me as I note above, and the new APIs I'm introducing are
also to help with PAT usage.
> That makes for a messy environment to work in, and it's messy enough already.
You're right about the mismatch over the kernel and even on a set of
family of APIs, that's a fair argument, but *that* is a very different
problem. Also the "messy environment" you describe is for proprietary
drivers and it always has been a messy environment for them, that's on
them and they should be talking to attorneys! The issue is already
super messy for them considering tons of folks using EXPORT_SYMBOL()
with the same intent as EXPORT_SYMBOL_GPL(), and refusing to use
EXPORT_SYMBOL_GPL() because of this.
> If we wanted to remove the EXPORT_SYMBOL/EXPORT_SYMBOL_GPL distinction
> completely, that'd be fine with me, too.
You're not the only one who has argued over this and the misfortune
over the naming used for EXPORT_SYMBOL_GPL(). Christoph made a similar
argument recently and provided some technical ideas on how to improve
the situation with symbol groups to reflect more of what was intended.
I also followed up with some further possibilities of how to do that
work [1]. If we really care about this so much perhaps we should talk
about this as a separate topic and address it but I would strongly
prefer to avoid this discussion at this point on this thread. If we
really want to we can talk about it over beers at Plumbers perhaps.
[1] http://lkml.kernel.org/r/[email protected]
> But as long as we keep it, I think it should mean something more than the preference of the author.
We extend the documentation as things become relevant and as you noted
to help with guidance, we did just that recently upon your request and
I provided basis for why things have changed over time now, as well as
reasoning by other maintainers on PAT interfaces, I hope this helps
clarify things.
> I know I did already ack this, and I even said I would merge it, but a
> month of thinking about this hasn't made me more comfortable with it,
> so I've changed my mind. I said before that I wouldn't try to stop
> you if you want to merge it some other way, but I don't want to ack
> it, and I don't want to merge it via my tree.
I appreciate your thoroughness over this matter and patience. I hope I
have provided new information to help you reconsider. Contrary to the
old days where we needed more of technical reason to use
EXPORT_SYMBOL_GPL() since its use has proven to have huge value, I
personally will always prefer to *always* use EXPORT_SYMBOL_GPL() for
all *new* exported symbols, unless explicitly told by the maintainer,
and even if they do ask for me to use EXPORT_SYMBOL_GPL() obviously
my intent remains the same, and no one can change that. These days
maintainer's don't ask me to change EXPORT_SYMBPOL_GPL() to
EXPORT_SYMBOL() though, and if they do they are of the position that
EXPORT_SYBOL() means the same thing as EXPORT_SYMBOL_GPL(), you're the
first to question this but it seems it was for the lack of guidance we
had to reflect new best practices.
I hope to have provided a bit of new information to help you
reconsider this series to go through you but since you seem to be fine
for this to go through another tree and since I failed to notice that
I should also get Arnd's Ack I am in hopes this might be able to go
through Arnd's tree if not through you. Please let me know, in case I
have to resubmit to Arnd.
Luis
On Fri, Jun 19, 2015 at 4:06 PM, Luis R. Rodriguez
<[email protected]> wrote:
> I hope to have provided a bit of new information to help you
> reconsider this series to go through you but since you seem to be fine
> for this to go through another tree and since I failed to notice that
> I should also get Arnd's Ack I am in hopes this might be able to go
> through Arnd's tree if not through you. Please let me know, in case I
> have to resubmit to Arnd.
If you want to have Arnd merge it, that's fine with me.
Bjorn