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From:   Patrick Venture <venture@google.com>
Date:   Mon, 4 Mar 2019 17:55:14 -0800
Message-ID: <CAO=notyY6QgKJ=OsQskH2FTaMHA+xTxuF-y7Y4g6G24o+QFXgQ@mail.gmail.com>
Subject: Re: [PATCH v5 2/2] drivers/misc: Add Aspeed P2A control driver
To:     Andrew Jeffery <andrew@aj.id.au>
Cc:     Arnd Bergmann <arnd@arndb.de>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Joel Stanley <joel@jms.id.au>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-arm-kernel@lists.infradead.org, linux-aspeed@lists.ozlabs.org
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Sender: linux-kernel-owner@vger.kernel.org
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On Mon, Mar 4, 2019 at 5:53 PM Andrew Jeffery <andrew@aj.id.au> wrote:
>
>
>
> On Tue, 5 Mar 2019, at 05:01, Patrick Venture wrote:
> > On Mon, Mar 4, 2019 at 7:45 AM Patrick Venture <venture@google.com> wrote:
> > >
> > > On Sun, Mar 3, 2019 at 4:04 PM Andrew Jeffery <andrew@aj.id.au> wrote:
> > > >
> > > > Hi Patrick.
> > > >
> > > > I've got some minor comments, otherwise it looks reasonable to me.
> > > >
> > > > On Thu, 28 Feb 2019, at 12:22, Patrick Venture wrote:
> > > > > The ASPEED AST2400, and AST2500 in some configurations include a
> > > > > PCI-to-AHB MMIO bridge.  This bridge allows a server to read and write
> > > > > in the BMC's physical address space.  This feature is especially useful
> > > > > when using this bridge to send large files to the BMC.
> > > > >
> > > > > The host may use this to send down a firmware image by staging data at a
> > > > > specific memory address, and in a coordinated effort with the BMC's
> > > > > software stack and kernel, transmit the bytes.
> > > > >
> > > > > This driver enables the BMC to unlock the PCI bridge on demand, and
> > > > > configure it via ioctl to allow the host to write bytes to an agreed
> > > > > upon location.  In the primary use-case, the region to use is known
> > > > > apriori on the BMC, and the host requests this information.  Once this
> > > > > request is received, the BMC's software stack will enable the bridge and
> > > > > the region and then using some software flow control (possibly via IPMI
> > > > > packets), copy the bytes down.  Once the process is complete, the BMC
> > > > > will disable the bridge and unset any region involved.
> > > > >
> > > > > The default behavior of this bridge when present is: enabled and all
> > > > > regions marked read-write.  This driver will fix the regions to be
> > > > > read-only and then disable the bridge entirely.
> > > > >
> > > > > The memory regions protected are:
> > > > >  * BMC flash MMIO window
> > > > >  * System flash MMIO windows
> > > > >  * SOC IO (peripheral MMIO)
> > > > >  * DRAM
> > > > >
> > > > > The DRAM region itself is all of DRAM and cannot be further specified.
> > > > > Once the PCI bridge is enabled, the host can read all of DRAM, and if
> > > > > the DRAM section is write-enabled, then it can write to all of it.
> > > > >
> > > > > Signed-off-by: Patrick Venture <venture@google.com>
> > > > > ---
> > > > > Changes for v5:
> > > > > - Fixup missing exit condition and remove extra jump.
> > > > > Changes for v4:
> > > > > - Added ioctl for reading back the memory-region configuration.
> > > > > - Cleaned up some unused variables.
> > > > > Changes for v3:
> > > > > - Deleted unused read and write methods.
> > > > > Changes for v2:
> > > > > - Dropped unused reads.
> > > > > - Moved call to disable bridge to before registering device.
> > > > > - Switch from using regs to using a syscon regmap. <<< IN PROGRESS
> > > > > - Updated the commit message. <<< TODO
> > > > > - Updated the bit flipped for SCU180_ENP2A
> > > > > - Dropped boolean region_specified variable.
> > > > > - Renamed p2a_ctrl in _probe to misc_ctrl per suggestion.
> > > > > - Renamed aspeed_p2a_region_search to aspeed_p2a_region_acquire
> > > > > - Updated commit message.
> > > > > ---
> > > > >  drivers/misc/Kconfig                 |   8 +
> > > > >  drivers/misc/Makefile                |   1 +
> > > > >  drivers/misc/aspeed-p2a-ctrl.c       | 456 +++++++++++++++++++++++++++
> > > > >  include/uapi/linux/aspeed-p2a-ctrl.h |  59 ++++
> > > > >  4 files changed, 524 insertions(+)
> > > > >  create mode 100644 drivers/misc/aspeed-p2a-ctrl.c
> > > > >  create mode 100644 include/uapi/linux/aspeed-p2a-ctrl.h
> > > > >
> > > > > diff --git a/drivers/misc/Kconfig b/drivers/misc/Kconfig
> > > > > index f417b06e11c5..9de1bafe5606 100644
> > > > > --- a/drivers/misc/Kconfig
> > > > > +++ b/drivers/misc/Kconfig
> > > > > @@ -485,6 +485,14 @@ config VEXPRESS_SYSCFG
> > > > >         bus. System Configuration interface is one of the possible means
> > > > >         of generating transactions on this bus.
> > > > >
> > > > > +config ASPEED_P2A_CTRL
> > > > > +     depends on (ARCH_ASPEED || COMPILE_TEST) && REGMAP && MFD_SYSCON
> > > > > +     tristate "Aspeed ast2400/2500 HOST P2A VGA MMIO to BMC bridge control"
> > > > > +     help
> > > > > +       Control Aspeed ast2400/2500 HOST P2A VGA MMIO to BMC mappings
> > > > > through
> > > > > +       ioctl()s, the driver also provides an interface for userspace
> > > > > mappings to
> > > > > +       a pre-defined region.
> > > > > +
> > > > >  config ASPEED_LPC_CTRL
> > > > >       depends on (ARCH_ASPEED || COMPILE_TEST) && REGMAP && MFD_SYSCON
> > > > >       tristate "Aspeed ast2400/2500 HOST LPC to BMC bridge control"
> > > > > diff --git a/drivers/misc/Makefile b/drivers/misc/Makefile
> > > > > index e39ccbbc1b3a..57577aee354f 100644
> > > > > --- a/drivers/misc/Makefile
> > > > > +++ b/drivers/misc/Makefile
> > > > > @@ -55,6 +55,7 @@ obj-$(CONFIG_VEXPRESS_SYSCFG)       += vexpress-syscfg.o
> > > > >  obj-$(CONFIG_CXL_BASE)               += cxl/
> > > > >  obj-$(CONFIG_ASPEED_LPC_CTRL)        += aspeed-lpc-ctrl.o
> > > > >  obj-$(CONFIG_ASPEED_LPC_SNOOP)       += aspeed-lpc-snoop.o
> > > > > +obj-$(CONFIG_ASPEED_P2A_CTRL)        += aspeed-p2a-ctrl.o
> > > > >  obj-$(CONFIG_PCI_ENDPOINT_TEST)      += pci_endpoint_test.o
> > > > >  obj-$(CONFIG_OCXL)           += ocxl/
> > > > >  obj-y                                += cardreader/
> > > > > diff --git a/drivers/misc/aspeed-p2a-ctrl.c
> > > > > b/drivers/misc/aspeed-p2a-ctrl.c
> > > > > new file mode 100644
> > > > > index 000000000000..6bde4f64632d
> > > > > --- /dev/null
> > > > > +++ b/drivers/misc/aspeed-p2a-ctrl.c
> > > > > @@ -0,0 +1,456 @@
> > > > > +/*
> > > > > + * Copyright 2019 Google Inc
> > > > > + *
> > > > > + * This program is free software; you can redistribute it and/or
> > > > > + * modify it under the terms of the GNU General Public License
> > > > > + * as published by the Free Software Foundation; either version
> > > > > + * 2 of the License, or (at your option) any later version.
> > > >
> > > > Should be a SPDX header instead.
> > >
> > > Ok, so delete the above and drop in:
> >
> > Was set straight on this.
> >
> > >
> > > """
> > > /* SPDX-License-Identifier: GPL-2.0+ WITH Linux-syscall-note */
> > > """
> > >
> > > Or just add that to the top above the Google GNU copyright line?  (I'm
> > > not a lawyer).
> > >
> > > >
> > > > > + *
> > > > > + * Provides a simple driver to control the ASPEED P2A interface which
> > > > > allows
> > > > > + * the host to read and write to various regions of the BMC's memory.
> > > > > + */
> > > > > +
> > > > > +#include <linux/fs.h>
> > > > > +#include <linux/io.h>
> > > > > +#include <linux/mfd/syscon.h>
> > > > > +#include <linux/miscdevice.h>
> > > > > +#include <linux/mm.h>
> > > > > +#include <linux/module.h>
> > > > > +#include <linux/mutex.h>
> > > > > +#include <linux/of_address.h>
> > > > > +#include <linux/of_device.h>
> > > > > +#include <linux/platform_device.h>
> > > > > +#include <linux/regmap.h>
> > > > > +#include <linux/slab.h>
> > > > > +#include <linux/uaccess.h>
> > > > > +
> > > > > +#include <linux/aspeed-p2a-ctrl.h>
> > > > > +
> > > > > +#define DEVICE_NAME  "aspeed-p2a-ctrl"
> > > > > +
> > > > > +/* SCU2C is a Misc. Control Register. */
> > > > > +#define SCU2C 0x2c
> > > > > +/* SCU180 is the PCIe Configuration Setting Control Register. */
> > > > > +#define SCU180 0x180
> > > > > +/* Bit 1 controls the P2A bridge, while bit 0 controls the entire VGA
> > > > > device
> > > > > + * on the PCI bus. */
> > > >
> > > > As this wraps to multiple lines the trailing `*/` should be on a separate line.
> > > > There are a few instances of this throughout.
> > >
> > > Can do.  I will also run checkpath -- I had done it initially, but I
> > > forgot on later editions.
> > >
> > > >
> > > > > +#define SCU180_ENP2A BIT(1)
> > > > > +
> > > > > +/* The ast2400/2500 both have six ranges. */
> > > > > +#define P2A_REGION_COUNT 6
> > > > > +
> > > > > +struct region {
> > > > > +     u32 min;
> > > > > +     u32 max;
> > > > > +     u32 bit;
> > > > > +};
> > > > > +
> > > > > +struct aspeed_p2a_model_data {
> > > > > +     /* min, max, bit */
> > > > > +     struct region regions[P2A_REGION_COUNT];
> > > > > +};
> > > > > +
> > > > > +struct aspeed_p2a_ctrl {
> > > > > +     struct miscdevice miscdev;
> > > > > +     struct regmap *regmap;
> > > > > +
> > > > > +     const struct aspeed_p2a_model_data *config;
> > > > > +
> > > > > +     /* Access to these needs to be locked, held via probe, mapping ioctl,
> > > > > +      * and release, remove.
> > > > > +      */
> > > > > +     struct mutex tracking;
> > > > > +     u32 readers;
> > > > > +     u32 readerwriters[P2A_REGION_COUNT];
> > > > > +
> > > > > +     phys_addr_t mem_base;
> > > > > +     resource_size_t mem_size;
> > > > > +};
> > > > > +
> > > > > +struct aspeed_p2a_user {
> > > > > +     struct file *file;
> > > > > +     struct aspeed_p2a_ctrl *parent;
> > > > > +
> > > > > +     /** The entire memory space is opened for reading once the bridge is
> > > > > +      * enabled, therefore this needs only to be tracked once per user.
> > > > > +      * If any user has it open for read, the bridge must stay enabled.
> > > > > +      */
> > > >
> > > > Generally the descriptions for the members are described in a kerneldoc
> > > > comment above the struct definition. Also you're mixing the kernel-doc
> > > > comment opener (`/**`) with non-kernel-doc comments (`/*` on the
> > > > tracking` mutex in `struct aspeed_p2a_ctrl` above).
> > >
> > > Ok, so anything that isn't really detailing the members, or functions,
> > > shouldn't be kerneldoc style.  Will fix throughout.
> > >
> > > >
> > > > > +     u32 read;
> > > > > +
> > > > > +     /** Each entry of the array corresponds to a P2A Region.  If the user
> > > > > +      * opens for read or readwrite, the reference goes up here.  On
> > > > > release,
> > > > > +      * this array is walked and references adjusted accordingly.
> > > > > +      */
> > > > > +     u32 readwrite[P2A_REGION_COUNT];
> > > > > +};
> > > > > +
> > > > > +static void aspeed_p2a_enable_bridge(struct aspeed_p2a_ctrl *p2a_ctrl)
> > > > > +{
> > > > > +     regmap_update_bits(p2a_ctrl->regmap, SCU180, SCU180_ENP2A,
> > > > > SCU180_ENP2A);
> > > >
> > > > Wrap this at 80 chars.
> > >
> > > Roger.
> > >
> > > >
> > > > > +}
> > > > > +
> > > > > +static void aspeed_p2a_disable_bridge(struct aspeed_p2a_ctrl *p2a_ctrl)
> > > > > +{
> > > > > +     regmap_update_bits(p2witha_ctrl->regmap, SCU180, SCU180_ENP2A, 0);
> > > > > +}
> > > > > +
> > > > > +static int aspeed_p2a_mmap(struct file *file, struct vm_area_struct
> > > > > *vma)
> > > > > +{
> > > > > +     struct aspeed_p2a_user *priv = file->private_data;
> > > > > +     struct aspeed_p2a_ctrl *ctrl = priv->parent;
> > > > > +
> > > > > +     if (ctrl->mem_base == 0 && ctrl->mem_size == 0)
> > > > > +             return -EINVAL;
> > > > > +
> > > > > +     unsigned long vsize = vma->vm_end - vma->vm_start;
> > > > > +     pgprot_t prot = vma->vm_page_prot;
> > > > > +
> > > > > +     if (vma->vm_pgoff + vsize > ctrl->mem_base + ctrl->mem_size)
> > > > > +             return -EINVAL;
> > > > > +
> > > > > +     /* ast2400/2500 AHB accesses are not cache coherent */
> > > > > +     prot = pgprot_noncached(prot);
> > > > > +
> > > > > +     if (remap_pfn_range(vma, vma->vm_start,
> > > > > +             (ctrl->mem_base >> PAGE_SHIFT) + vma->vm_pgoff,
> > > > > +             vsize, prot))
> > > > > +             return -EAGAIN;
> > > > > +
> > > > > +     return 0;
> > > > > +}
> > > > > +
> > > > > +static void aspeed_p2a_region_acquire(struct aspeed_p2a_user *priv,
> > > > > +             struct aspeed_p2a_ctrl *ctrl,
> > > > > +             struct aspeed_p2a_ctrl_mapping *map)
> > > > > +{
> > > > > +     int i;
> > > > > +     u32 base, end;
> > > > > +
> > > > > +     base = map->addr;
> > > > > +     end = map->addr + (map->length - 1);
> > > > > +
> > > > > +     /* If the value is a legal u32, it will find a match. */
> > > > > +     for (i = 0; i < P2A_REGION_COUNT; i++) {
> > > > > +             const struct region *curr = &ctrl->config->regions[i];
> > > > > +
> > > > > +             /* If the top of this region is lower than your base, skip it.
> > > > > +              */
> > > > > +             if (curr->max < base)
> > > > > +                     continue;
> > > > > +
> > > > > +             /* If the bottom of this region is higher than your end, bail.
> > > > > +              */
> > > > > +             if (curr->min > end)
> > > > > +                     break;
> > > > > +             /* Lock this and update it, therefore it someone else is
> > > > > +              * closing their file out, this'll preserve the increment.
> > > > > +              */
> > > > > +             mutex_lock(&ctrl->tracking);
> > > > > +             ctrl->readerwriters[i] += 1;
> > > > > +             mutex_unlock(&ctrl->tracking);
> > > > > +
> > > > > +             /* Track with the user, so when they close their file, we can
> > > > > +              * decrement properly.
> > > > > +              */
> > > >
> > > > The comments about tracking for decrement-on-release purposes is
> > > > useful, but I think the other comments in this loop are probably
> > > > unnecessary. Up to you though.
> > >
> > > I've often found drivers under-documented, so I went in the other direction.
> > >
> > > >
> > > > > +             priv->readwrite[i] += 1;
> > > > > +
> > > > > +             /* Enable the region as read-write. */
> > > > > +             regmap_update_bits(ctrl->regmap, SCU2C, curr->bit, 0);
> > > > > +     }
> > > > > +}
> > > > > +
> > > > > +static long aspeed_p2a_ioctl(struct file *file, unsigned int cmd,
> > > > > +             unsigned long data)
> > > > > +{
> > > > > +     struct aspeed_p2a_user *priv = file->private_data;
> > > > > +     struct aspeed_p2a_ctrl *ctrl = priv->parent;
> > > > > +     void __user *arg = (void __user *)data;
> > > > > +     struct aspeed_p2a_ctrl_mapping map;
> > > > > +
> > > > > +     if (copy_from_user(&map, arg, sizeof(map)))
> > > > > +             return -EFAULT;
> > > > > +
> > > > > +     switch (cmd) {
> > > > > +     case ASPEED_P2A_CTRL_IOCTL_SET_WINDOW:
> > > > > +             /* If they want a region to be read-only, since the entire
> > > > > +              * region is read-only once enabled, we just need to track this
> > > > > +              * user wants to read from the bridge, and if it's not enabled.
> > > > > +              * Enable it.
> > > > > +              */
> > > > > +             if (map.flags == ASPEED_P2A_CTRL_READ_ONLY) {
> > > > > +                     mutex_lock(&ctrl->tracking);
> > > > > +                     ctrl->readers += 1;
> > > > > +                     mutex_unlock(&ctrl->tracking);
> > > > > +
> > > > > +                     /* Track with the user, so when they close their file,
> > > > > +                      * we can decrement properly.
> > > > > +                      */
> > > > > +                     priv->read += 1;
> > > > > +             } else if (map.flags == ASPEED_P2A_CTRL_READWRITE) {
> > > > > +                     aspeed_p2a_region_acquire(priv, ctrl, &map);
> > > > > +             } else {
> > > > > +                     /* Invalid map flags. */
> > > > > +                     return -EINVAL;
> > > > > +             }
> > > > > +
> > > > > +             aspeed_p2a_enable_bridge(ctrl);
> > > > > +             return 0;
> > > > > +     case ASPEED_P2A_CTRL_IOCTL_GET_MEMORY_CONFIG:
> > > > > +             /* This is a request for the memory-region and corresponding
> > > > > +              * length that is used by the driver for mmap. */
> > > > > +
> > > > > +             map.flags = 0;
> > > > > +             map.addr = ctrl->mem_base;
> > > > > +             map.length = ctrl->mem_size;
> > > >
> > > > Thinking out loud here - do we want to allow ourselves an escape hatch
> > > > for supporting multiple reserved memory locations? Otherwise we might
> > > > need a new ioctl() for it. On the flip-side, not actually having this use-case
> > > > means we might break the implementation anyway, so it could be a
> > > > double-edged sword. Thoughts?
> > >
> > > How about this, I use a different structure that has an index -- so
> > > you pass in the structure with the index set, requesting the region
> > > information, and it returns the details for that memory-region until
> > > the index exceeds the number of regions and returns -ENODEV.
> > >
> > > However, to avoid extra complexity today, the dts will only support
> > > one memory region...  The complexity of dealing with checking what
> > > region they want to use in mmap by checking what region has been
> > > enabled by that specific user may be too much of a pain though for the
> > > probable life of this driver.  So yeah, a bit of a double-edged sword
> > > of complexity to approach the extra complexity even partially.  I
> > > think having one memory-region is fine for now, and I can't see the
> > > future.  Perhaps having the ioctl structure change and no other
> > > changes is sufficient while being extendable in the future if
> > > someone's need should arise.  That way there won't be an obsolete
> > > ioctl or ambiguous ioctl (code that calls the old one and its result
> > > is quasi-incorrect).
> > >
> > > >
> > > > > +
> > > > > +             return copy_to_user(arg, &map, sizeof(map)) ? -EFAULT : 0;
> > > > > +     }
> > > > > +
> > > > > +     return -EINVAL;
> > > > > +}
> > > > > +
> > > > > +
> > > > > +/**
> > > > > + * When a user opens this file, we create a structure to track their
> > > > > mappings.
> > > > > + *
> > > > > + * A user can map a region as read-only (bridge enabled), or
> > > > > read-write (bit
> > > > > + * flipped, and bridge enabled).  Either way, this tracking is used,
> > > > > s.t. when
> > > > > + * they release the device references are handled.
> > > > > + *
> > > > > + * The bridge is not enabled until a user calls an ioctl to map a
> > > > > region,
> > > > > + * simply opening the device does not enable it.
> > > > > + */
> > > > > +static int aspeed_p2a_open(struct inode *inode, struct file *file)
> > > > > +{
> > > > > +     struct aspeed_p2a_user *priv;
> > > > > +
> > > > > +     priv = kmalloc(sizeof(*priv), GFP_KERNEL);
> > > > > +     if (!priv)
> > > > > +             return -ENOMEM;
> > > > > +
> > > > > +     priv->file = file;
> > > > > +     priv->read = 0;
> > > > > +     memset(priv->readwrite, 0, sizeof(priv->readwrite));
> > > > > +
> > > > > +     /* The file's private_data is initialized to the p2a_ctrl. */
> > > > > +     priv->parent = file->private_data;
> > > > > +
> > > > > +     /* Set the file's private_data to the user's data. */
> > > > > +     file->private_data = priv;
> > > > > +
> > > > > +     return 0;
> > > > > +}
> > > > > +
> > > > > +/**
> > > > > + * This will close the users mappings.  It will go through what they
> > > > > had opened
> > > > > + * for readwrite, and decrement those counts.  If at the end, this is
> > > > > the last
> > > > > + * user, it'll close the bridge.
> > > > > + */
> > > > > +static int aspeed_p2a_release(struct inode *inode, struct file *file)
> > > > > +{
> > > > > +     int i;
> > > > > +     u32 value;
> > > > > +     u32 bits = 0;
> > > > > +     bool open_regions = false;
> > > > > +     struct aspeed_p2a_user *priv = file->private_data;
> > > > > +
> > > > > +     /* Lock others from changing these values until everything is updated
> > > > > +      * in one pass */
> > > > > +     mutex_lock(&priv->parent->tracking);
> > > > > +
> > > > > +     priv->parent->readers -= priv->read;;
> > > > > +
> > > > > +     for (i = 0; i < P2A_REGION_COUNT; i++) {
> > > > > +             priv->parent->readerwriters[i] -= priv->readwrite[i];
> > > > > +
> > > > > +             if (priv->parent->readerwriters[i] > 0)
> > > > > +                     open_regions = true;
> > > > > +             else
> > > > > +                     bits |= priv->parent->config->regions[i].bit;
> > > > > +     }
> > > > > +
> > > > > +     /* Setting a bit to 1 disables the region, so let's just OR with the
> > > > > +      * above to disable any.
> > > > > +      */
> > > > > +
> > > > > +     /* Note, if another user is trying to ioctl, they can't grab tracking,
> > > > > +      * and therefore can't grab either register mutex.
> > > > > +      * If another user is trying to close, they can't grab tracking
> > > > > either.
> > > > > +      */
> > > > > +     regmap_update_bits(priv->parent->regmap, SCU2C, bits, bits);
> > > > > +
> > > > > +     /* If parent->readers is zero and open windows is 0, disable the
> > > > > +      * bridge.
> > > > > +      */
> > > > > +     if (!open_regions && priv->parent->readers == 0)
> > > > > +             aspeed_p2a_disable_bridge(priv->parent);
> > > > > +
> > > > > +     mutex_unlock(&priv->parent->tracking);
> > > > > +
> > > > > +     kfree(priv);
> > > > > +
> > > > > +     return 0;
> > > > > +}
> > > > > +
> > > > > +static const struct file_operations aspeed_p2a_ctrl_fops = {
> > > > > +     .owner = THIS_MODULE,
> > > > > +     .mmap = aspeed_p2a_mmap,
> > > > > +     .unlocked_ioctl = aspeed_p2a_ioctl,
> > > > > +     .open = aspeed_p2a_open,
> > > > > +     .release = aspeed_p2a_release,
> > > > > +};
> > > > > +
> > > > > +/** The regions are controlled by SCU2C */
> > > > > +static void aspeed_p2a_disable_all(struct aspeed_p2a_ctrl *p2a_ctrl)
> > > > > +{
> > > > > +     int i;
> > > > > +     u32 value = 0;
> > > > > +
> > > > > +     for (i = 0; i < P2A_REGION_COUNT; i++)
> > > > > +             value |= p2a_ctrl->config->regions[i].bit;
> > > > > +
> > > > > +     regmap_update_bits(p2a_ctrl->regmap, SCU2C, value, value);
> > > > > +
> > > > > +     /* Disable the bridge. */
> > > > > +     aspeed_p2a_disable_bridge(p2a_ctrl);
> > > > > +}
> > > > > +
> > > > > +static int aspeed_p2a_ctrl_probe(struct platform_device *pdev)
> > > > > +{
> > > > > +     struct aspeed_p2a_ctrl *misc_ctrl;
> > > > > +     struct device *dev;
> > > > > +     struct resource *res, resm;
> > > > > +     struct device_node *node;
> > > > > +     int rc = 0;
> > > > > +
> > > > > +     dev = &pdev->dev;
> > > > > +
> > > > > +     misc_ctrl = devm_kzalloc(dev, sizeof(*misc_ctrl), GFP_KERNEL);
> > > > > +     if (!misc_ctrl)
> > > > > +             return -ENOMEM;
> > > > > +
> > > > > +     mutex_init(&misc_ctrl->tracking);
> > > > > +     misc_ctrl->readers = 0;
> > > > > +     memset(misc_ctrl->readerwriters, 0, sizeof(misc_ctrl->readerwriters));
> > > > > +
> > > > > +     misc_ctrl->mem_size = 0;
> > > > > +     misc_ctrl->mem_base = 0;
> > > > > +
> > > > > +     /* optional. */
> > > > > +     node = of_parse_phandle(dev->of_node, "memory-region", 0);
> > > > > +     if (node) {
> > > > > +             rc = of_address_to_resource(node, 0, &resm);
> > > > > +             of_node_put(node);
> > > > > +             if (rc) {
> > > > > +                     dev_err(dev, "Couldn't address to resource for reserved memory\n");
> > > >
> > > > I think the message could be improved, something like "No reserved memory
> > > > specified". Having said that, I don't think it should be an error condition either;
> > > > our experience with aspeed-lpc-ctrl was that it was useful for the memory-region
> > > > property to be optional. You already have:
> > >
> > > Ok.
> >
> > Ok, when I read this, I see it as an error condition.  In this case
> > the node was specified but was invalid.
>
> Sorry, yeah you're right. I'm going to blame a 6-week old child and a lack of sleep :)

Haha. No worries!  Thanks for all your time reviewing this.  I really
appreciate your cycles on this.

>
> Cheers,
>
> Andrew
>
> >
> > >
> > > >
> > > > > +
> > > > > +     if (ctrl->mem_base == 0 && ctrl->mem_size == 0)
> > > > > +             return -EINVAL;
> > > >
> > > > in the mmap() callback, but we don't get that far unless someone has specified a
> > > > zero-sized reserved-memory node. I think supporting memory-region as optional
> > > > is just a matter of adding the same check to the GET_MEMORY_CONFIG ioctl().
> > > >
> > > > > +                     return -ENOMEM;
> > > >
> > > > The system isn't out of memory so this isn't an ENOMEM condition. I think ENODEV
> > > > is more appropriate, but if we make the memory region optional then this goes
> > > > away anyway.
> > >
> > > Roger.
> > >
> > > >
> > > > > +             }
> > > > > +
> > > > > +             misc_ctrl->mem_size = resource_size(&resm);
> > > > > +             misc_ctrl->mem_base = resm.start;
> > > > > +     }
> > > > > +
> > > > > +     node = of_parse_phandle(dev->of_node, "syscon", 0);
> > > > > +     if (!node) {
> > > > > +             dev_err(dev, "Couldn't find syscon property\n");
> > > > > +             return -ENODEV;
> > > > > +     }
> > > > > +
> > > > > +     misc_ctrl->regmap = syscon_node_to_regmap(node);
> > > > > +     if (IS_ERR(misc_ctrl->regmap)) {
> > > > > +             dev_err(dev, "Couldn't get regmap\n");
> > > > > +             return -ENODEV;
> > > > > +     }
> > > > > +     of_node_put(node);
> > > > > +
> > > > > +     misc_ctrl->config = of_device_get_match_data(dev);
> > > > > +
> > > > > +     dev_set_drvdata(&pdev->dev, misc_ctrl);
> > > > > +
> > > > > +     aspeed_p2a_disable_all(misc_ctrl);
> > > > > +
> > > > > +     misc_ctrl->miscdev.minor = MISC_DYNAMIC_MINOR;
> > > > > +     misc_ctrl->miscdev.name = DEVICE_NAME;
> > > > > +     misc_ctrl->miscdev.fops = &aspeed_p2a_ctrl_fops;
> > > > > +     misc_ctrl->miscdev.parent = dev;
> > > > > +
> > > > > +     rc = misc_register(&misc_ctrl->miscdev);
> > > > > +     if (rc)
> > > > > +             dev_err(dev, "Unable to register device\n");
> > > > > +
> > > > > +     return rc;
> > > > > +}
> > > > > +
> > > > > +static int aspeed_p2a_ctrl_remove(struct platform_device *pdev)
> > > > > +{
> > > > > +     struct aspeed_p2a_ctrl *p2a_ctrl = dev_get_drvdata(&pdev->dev);
> > > > > +
> > > > > +     misc_deregister(&p2a_ctrl->miscdev);
> > > > > +
> > > > > +     return 0;
> > > > > +}
> > > > > +
> > > > > +/*
> > > > > + * bit | SCU2C | ast2400
> > > > > + *  25 | DRAM  | 0x40000000 - 0x5FFFFFFF
> > > > > + *  24 | SPI   | 0x30000000 - 0x3FFFFFFF
> > > > > + *  23 | SOC   | 0x18000000 - 0x1FFFFFFF, 0x60000000 - 0xFFFFFFFF
> > > > > + *  22 | FLASH | 0x00000000 - 0x17FFFFFF, 0x20000000 - 0x2FFFFFFF
> > > > > + *
> > > > > + * bit | SCU2C | ast2500
> > > > > + *  25 | DRAM  | 0x80000000 - 0xFFFFFFFF
> > > > > + *  24 | SPI   | 0x60000000 - 0x7FFFFFFF
> > > > > + *  23 | SOC   | 0x10000000 - 0x1FFFFFFF, 0x40000000 - 0x5FFFFFFF
> > > > > + *  22 | FLASH | 0x00000000 - 0x0FFFFFFF, 0x20000000 - 0x3FFFFFFF
> > > > > + */
> > > >
> > > > The comment is probably unnecessary given the structure declarations
> > > > below.
> > >
> > > Fair enough, will drop it.
> > >
> > > >
> > > > > +
> > > > > +#define SCU2C_DRAM   BIT(25)
> > > > > +#define SCU2C_SPI    BIT(24)
> > > > > +#define SCU2C_SOC    BIT(23)
> > > > > +#define SCU2C_FLASH  BIT(22)
> > > > > +
> > > > > +static const struct aspeed_p2a_model_data ast2400_model_data = {
> > > > > +     .regions = {
> > > > > +             {0x00000000, 0x17FFFFFF, SCU2C_FLASH},
> > > > > +             {0x18000000, 0x1FFFFFFF, SCU2C_SOC},
> > > > > +             {0x20000000, 0x2FFFFFFF, SCU2C_FLASH},
> > > > > +             {0x30000000, 0x3FFFFFFF, SCU2C_SPI},
> > > > > +             {0x40000000, 0x5FFFFFFF, SCU2C_DRAM},
> > > > > +             {0x60000000, 0xFFFFFFFF, SCU2C_SOC},
> > > > > +     }
> > > > > +};
> > > > > +
> > > > > +static const struct aspeed_p2a_model_data ast2500_model_data = {
> > > > > +     .regions = {
> > > > > +             {0x00000000, 0x0FFFFFFF, SCU2C_FLASH},
> > > > > +             {0x10000000, 0x1FFFFFFF, SCU2C_SOC},
> > > > > +             {0x20000000, 0x3FFFFFFF, SCU2C_FLASH},
> > > > > +             {0x40000000, 0x5FFFFFFF, SCU2C_SOC},
> > > > > +             {0x60000000, 0x7FFFFFFF, SCU2C_SPI},
> > > > > +             {0x80000000, 0xFFFFFFFF, SCU2C_DRAM},
> > > > > +     }
> > > > > +};
> > > > > +
> > > > > +static const struct of_device_id aspeed_p2a_ctrl_match[] = {
> > > > > +     { .compatible = "aspeed,ast2400-p2a-ctrl",
> > > > > +       .data = &ast2400_model_data },
> > > > > +     { .compatible = "aspeed,ast2500-p2a-ctrl",
> > > > > +       .data = &ast2500_model_data },
> > > > > +     { },
> > > > > +};
> > > > > +
> > > > > +static struct platform_driver aspeed_p2a_ctrl_driver = {
> > > > > +     .driver = {
> > > > > +             .name           = DEVICE_NAME,
> > > > > +             .of_match_table = aspeed_p2a_ctrl_match,
> > > > > +     },
> > > > > +     .probe = aspeed_p2a_ctrl_probe,
> > > > > +     .remove = aspeed_p2a_ctrl_remove,
> > > > > +};
> > > > > +
> > > > > +module_platform_driver(aspeed_p2a_ctrl_driver);
> > > > > +
> > > > > +MODULE_DEVICE_TABLE(of, aspeed_p2a_ctrl_match);
> > > > > +MODULE_LICENSE("GPL");
> > > > > +MODULE_AUTHOR("Patrick Venture <venture@google.com>");
> > > > > +MODULE_DESCRIPTION("Control for aspeed 2400/2500 P2A VGA HOST to BMC
> > > > > mappings");
> > > > > diff --git a/include/uapi/linux/aspeed-p2a-ctrl.h
> > > > > b/include/uapi/linux/aspeed-p2a-ctrl.h
> > > > > new file mode 100644
> > > > > index 000000000000..e839cdc31db9
> > > > > --- /dev/null
> > > > > +++ b/include/uapi/linux/aspeed-p2a-ctrl.h
> > > > > @@ -0,0 +1,59 @@
> > > > > +/* SPDX-License-Identifier: GPL-2.0+ WITH Linux-syscall-note */
> > > > > +/*
> > > > > + * Copyright 2019 Google Inc
> > > > > + *
> > > > > + * This program is free software; you can redistribute it and/or
> > > > > + * modify it under the terms of the GNU General Public License
> > > > > + * as published by the Free Software Foundation; either version
> > > > > + * 2 of the License, or (at your option) any later version.
> > > >
> > > > SPDX again.
> > >
> > > So, only SPDX?  I'm not super on the ball with this type of thing.  I
> > > just mirrored what I saw in other recent aspeed drivers.
> > >
> > > >
> > > > > + *
> > > > > + * Provides a simple driver to control the ASPEED P2A interface which
> > > > > allows
> > > > > + * the host to read and write to various regions of the BMC's memory.
> > > > > + */
> > > > > +
> > > > > +#ifndef _UAPI_LINUX_ASPEED_P2A_CTRL_H
> > > > > +#define _UAPI_LINUX_ASPEED_P2A_CTRL_H
> > > > > +
> > > > > +#include <linux/ioctl.h>
> > > > > +#include <linux/types.h>
> > > > > +
> > > > > +#define ASPEED_P2A_CTRL_READ_ONLY 0
> > > > > +#define ASPEED_P2A_CTRL_READWRITE 1
> > > > > +
> > > > > +/*
> > > > > + * This driver provides a mechanism for enabling or disabling the
> > > > > read-write
> > > > > + * property of specific windows into the ASPEED BMC's memory.
> > > > > + *
> > > > > + * A user can map a region of the BMC's memory as read-only or
> > > > > read-write, with
> > > > > + * the caveat that once any region is mapped, all regions are unlocked
> > > > > for
> > > > > + * reading.
> > > > > + */
> > > > > +
> > > > > +/**
> > > > > + * Unlock a region of BMC physical memory for access from the host.
> > > > > + *
> > > > > + * Also used to read back the optional memory-region configuration for
> > > > > the
> > > > > + * driver.
> > > > > + */
> > > > > +struct aspeed_p2a_ctrl_mapping {
> > > > > +     __u32 addr;
> > > > > +     __u32 length;
> > > > > +     __u32 flags;
> > > > > +};
> > > > > +
> > > > > +#define __ASPEED_P2A_CTRL_IOCTL_MAGIC 0xb3
> > > > > +
> > > > > +/**
> > > > > + * This IOCTL is meant to configure a region or regions of memory
> > > > > given a
> > > > > + * starting address and length to be readable by the host, or
> > > > > + * readable-writeable. */
> > > > > +#define ASPEED_P2A_CTRL_IOCTL_SET_WINDOW
> > > > > _IOW(__ASPEED_P2A_CTRL_IOCTL_MAGIC, \
> > > > > +             0x00, struct aspeed_p2a_ctrl_mapping)
> > > > > +
> > > > > +/**
> > > > > + * This IOCTL is meant to read back to the user the base address and
> > > > > length of
> > > > > + * the memory-region specified to the driver for use with mmap. */
> > > > > +#define ASPEED_P2A_CTRL_IOCTL_GET_MEMORY_CONFIG
> > > > > _IOWR(__ASPEED_P2A_CTRL_IOCTL_MAGIC, \
> > > >
> > > > Wrap this at 80?
> > > >
> > > > Cheers,
> > > >
> > > > Andrew
> > > >
> > > > > +             0x01, struct aspeed_p2a_ctrl_mapping)
> > > > > +
> > > > > +#endif /* _UAPI_LINUX_ASPEED_P2A_CTRL_H */
> > > > > --
> > > > > 2.21.0.rc2.261.ga7da99ff1b-goog
> > > > >
> > > > >
> >