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Date:   Sat, 29 Dec 2018 12:16:47 +1100 (AEDT)
From:   Finn Thain <fthain@telegraphics.com.au>
To:     LEROY Christophe <christophe.leroy@c-s.fr>
cc:     linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
        linux-m68k@lists.linux-m68k.org,
        Geert Uytterhoeven <geert@linux-m68k.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Arnd Bergmann <arnd@arndb.de>
Subject: Re: [PATCH v8 02/25] m68k/atari: Move Atari-specific code out of
 drivers/char/nvram.c
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On Fri, 28 Dec 2018, LEROY Christophe wrote:

> Finn Thain <fthain@telegraphics.com.au> a ?crit?:
> 
> > Move the m68k-specific code out of the driver to make the driver generic.
> >
> > I've used 'SPDX-License-Identifier: GPL-2.0+' for the new file because the
> > old file is covered by MODULE_LICENSE("GPL").
> >
> > Signed-off-by: Finn Thain <fthain@telegraphics.com.au>
> > Tested-by: Christian T. Steigies <cts@debian.org>
> > Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>
> > ---
> > Changed since v7:
> >  - Added SPDX-License-Identifier.
> > ---
> >  arch/m68k/atari/Makefile |   2 +
> >  arch/m68k/atari/nvram.c  | 243 +++++++++++++++++++++++++++++++++
> >  drivers/char/nvram.c     | 280 +++++----------------------------------
> >  3 files changed, 280 insertions(+), 245 deletions(-)
> >  create mode 100644 arch/m68k/atari/nvram.c
> >
> > diff --git a/arch/m68k/atari/Makefile b/arch/m68k/atari/Makefile
> > index 0cac723306f9..0b86bb6cfa87 100644
> > --- a/arch/m68k/atari/Makefile
> > +++ b/arch/m68k/atari/Makefile
> > @@ -6,3 +6,5 @@ obj-y		:= config.o time.o debug.o ataints.o stdma.o \
> >  			atasound.o stram.o
> >
> >  obj-$(CONFIG_ATARI_KBD_CORE)	+= atakeyb.o
> > +
> > +obj-$(CONFIG_NVRAM:m=y)		+= nvram.o
> > diff --git a/arch/m68k/atari/nvram.c b/arch/m68k/atari/nvram.c
> > new file mode 100644
> > index 000000000000..3e620ee955ba
> > --- /dev/null
> > +++ b/arch/m68k/atari/nvram.c
> > @@ -0,0 +1,243 @@
> > +// SPDX-License-Identifier: GPL-2.0+
> > +/*
> > + * CMOS/NV-RAM driver for Atari. Adapted from drivers/char/nvram.c.
> > + * Copyright (C) 1997 Roman Hodek <Roman.Hodek@informatik.uni-erlangen.de>
> > + * idea by and with help from Richard Jelinek <rj@suse.de>
> > + * Portions copyright (c) 2001,2002 Sun Microsystems (thockin@sun.com)
> > + * Further contributions from Cesar Barros, Erik Gilling, Tim Hockin and
> > + * Wim Van Sebroeck.
> > + */
> > +
> > +#include <linux/errno.h>
> > +#include <linux/init.h>
> > +#include <linux/mc146818rtc.h>
> > +#include <linux/module.h>
> > +#include <linux/nvram.h>
> > +#include <linux/proc_fs.h>
> > +#include <linux/seq_file.h>
> > +#include <linux/spinlock.h>
> > +#include <linux/types.h>
> > +#include <asm/atarihw.h>
> > +#include <asm/atariints.h>
> > +
> > +#define NVRAM_BYTES		50
> > +
> > +/* It is worth noting that these functions all access bytes of general
> > + * purpose memory in the NVRAM - that is to say, they all add the
> > + * NVRAM_FIRST_BYTE offset. Pass them offsets into NVRAM as if you did not
> > + * know about the RTC cruft.
> > + */
> > +
> > +/* Note that *all* calls to CMOS_READ and CMOS_WRITE must be done with
> > + * rtc_lock held. Due to the index-port/data-port design of the RTC, we
> > + * don't want two different things trying to get to it at once. (e.g. the
> > + * periodic 11 min sync from kernel/time/ntp.c vs. this driver.)
> > + */
> > +
> > +unsigned char __nvram_read_byte(int i)
> > +{
> > +	return CMOS_READ(NVRAM_FIRST_BYTE + i);
> > +}
> > +
> > +unsigned char nvram_read_byte(int i)
> > +{
> > +	unsigned long flags;
> > +	unsigned char c;
> > +
> > +	spin_lock_irqsave(&rtc_lock, flags);
> > +	c = __nvram_read_byte(i);
> > +	spin_unlock_irqrestore(&rtc_lock, flags);
> > +	return c;
> > +}
> > +EXPORT_SYMBOL(nvram_read_byte);
> > +
> > +/* This races nicely with trying to read with checksum checking */
> > +void __nvram_write_byte(unsigned char c, int i)
> > +{
> > +	CMOS_WRITE(c, NVRAM_FIRST_BYTE + i);
> > +}
> > +
> > +void nvram_write_byte(unsigned char c, int i)
> > +{
> > +	unsigned long flags;
> > +
> > +	spin_lock_irqsave(&rtc_lock, flags);
> > +	__nvram_write_byte(c, i);
> > +	spin_unlock_irqrestore(&rtc_lock, flags);
> > +}
> > +
> > +/* On Ataris, the checksum is over all bytes except the checksum bytes
> > + * themselves; these are at the very end.
> > + */
> > +#define ATARI_CKS_RANGE_START	0
> > +#define ATARI_CKS_RANGE_END	47
> > +#define ATARI_CKS_LOC		48
> > +
> > +int __nvram_check_checksum(void)
> > +{
> > +	int i;
> > +	unsigned char sum = 0;
> > +
> > +	for (i = ATARI_CKS_RANGE_START; i <= ATARI_CKS_RANGE_END; ++i)
> > +		sum += __nvram_read_byte(i);
> > +	return (__nvram_read_byte(ATARI_CKS_LOC) == (~sum & 0xff)) &&
> > +	       (__nvram_read_byte(ATARI_CKS_LOC + 1) == (sum & 0xff));
> > +}
> > +
> > +int nvram_check_checksum(void)
> > +{
> > +	unsigned long flags;
> > +	int rv;
> > +
> > +	spin_lock_irqsave(&rtc_lock, flags);
> > +	rv = __nvram_check_checksum();
> > +	spin_unlock_irqrestore(&rtc_lock, flags);
> > +	return rv;
> > +}
> > +EXPORT_SYMBOL(nvram_check_checksum);
> > +
> > +static void __nvram_set_checksum(void)
> > +{
> > +	int i;
> > +	unsigned char sum = 0;
> > +
> > +	for (i = ATARI_CKS_RANGE_START; i <= ATARI_CKS_RANGE_END; ++i)
> > +		sum += __nvram_read_byte(i);
> > +	__nvram_write_byte(~sum, ATARI_CKS_LOC);
> > +	__nvram_write_byte(sum, ATARI_CKS_LOC + 1);
> > +}
> > +
> > +#ifdef CONFIG_PROC_FS
> > +static struct {
> > +	unsigned char val;
> > +	const char *name;
> > +} boot_prefs[] = {
> > +	{ 0x80, "TOS" },
> > +	{ 0x40, "ASV" },
> > +	{ 0x20, "NetBSD (?)" },
> > +	{ 0x10, "Linux" },
> > +	{ 0x00, "unspecified" },
> > +};
> > +
> > +static const char * const languages[] = {
> > +	"English (US)",
> > +	"German",
> > +	"French",
> > +	"English (UK)",
> > +	"Spanish",
> > +	"Italian",
> > +	"6 (undefined)",
> > +	"Swiss (French)",
> > +	"Swiss (German)",
> > +};
> > +
> > +static const char * const dateformat[] = {
> > +	"MM%cDD%cYY",
> > +	"DD%cMM%cYY",
> > +	"YY%cMM%cDD",
> > +	"YY%cDD%cMM",
> > +	"4 (undefined)",
> > +	"5 (undefined)",
> > +	"6 (undefined)",
> > +	"7 (undefined)",
> > +};
> > +
> > +static const char * const colors[] = {
> > +	"2", "4", "16", "256", "65536", "??", "??", "??"
> > +};
> > +
> > +static void atari_nvram_proc_read(unsigned char *nvram, struct  
> > seq_file *seq,
> > +				  void *offset)
> > +{
> > +	int checksum;
> > +	int i;
> > +	unsigned int vmode;
> > +
> > +	spin_lock_irq(&rtc_lock);
> > +	checksum = __nvram_check_checksum();
> > +	spin_unlock_irq(&rtc_lock);
> > +
> > +	seq_printf(seq, "Checksum status  : %svalid\n", checksum ? "" : "not ");
> > +
> > +	seq_puts(seq, "Boot preference  : ");
> > +	for (i = ARRAY_SIZE(boot_prefs) - 1; i >= 0; --i)
> > +		if (nvram[1] == boot_prefs[i].val) {
> > +			seq_printf(seq, "%s\n", boot_prefs[i].name);
> > +			break;
> > +		}
> > +	if (i < 0)
> > +		seq_printf(seq, "0x%02x (undefined)\n", nvram[1]);
> > +
> > +	seq_printf(seq, "SCSI arbitration : %s\n",
> > +		   (nvram[16] & 0x80) ? "on" : "off");
> > +	seq_puts(seq, "SCSI host ID     : ");
> > +	if (nvram[16] & 0x80)
> > +		seq_printf(seq, "%d\n", nvram[16] & 7);
> > +	else
> > +		seq_puts(seq, "n/a\n");
> > +
> > +	if (!MACH_IS_FALCON)
> > +		return;
> > +
> > +	seq_puts(seq, "OS language      : ");
> > +	if (nvram[6] < ARRAY_SIZE(languages))
> > +		seq_printf(seq, "%s\n", languages[nvram[6]]);
> > +	else
> > +		seq_printf(seq, "%u (undefined)\n", nvram[6]);
> > +	seq_puts(seq, "Keyboard language: ");
> > +	if (nvram[7] < ARRAY_SIZE(languages))
> > +		seq_printf(seq, "%s\n", languages[nvram[7]]);
> > +	else
> > +		seq_printf(seq, "%u (undefined)\n", nvram[7]);
> > +	seq_puts(seq, "Date format      : ");
> > +	seq_printf(seq, dateformat[nvram[8] & 7],
> > +		   nvram[9] ? nvram[9] : '/', nvram[9] ? nvram[9] : '/');
> > +	seq_printf(seq, ", %dh clock\n", nvram[8] & 16 ? 24 : 12);
> > +	seq_puts(seq, "Boot delay       : ");
> > +	if (nvram[10] == 0)
> > +		seq_puts(seq, "default");
> > +	else
> > +		seq_printf(seq, "%ds%s\n", nvram[10],
> > +			   nvram[10] < 8 ? ", no memory test" : "");
> > +
> > +	vmode = (nvram[14] << 8) | nvram[15];
> > +	seq_printf(seq,
> > +		   "Video mode       : %s colors, %d columns, %s %s monitor\n",
> > +		   colors[vmode & 7], vmode & 8 ? 80 : 40,
> > +		   vmode & 16 ? "VGA" : "TV", vmode & 32 ? "PAL" : "NTSC");
> > +	seq_printf(seq,
> > +		   "                   %soverscan, compat. mode %s%s\n",
> > +		   vmode & 64 ? "" : "no ", vmode & 128 ? "on" : "off",
> > +		   vmode & 256 ?
> > +		   (vmode & 16 ? ", line doubling" : ", half screen") : "");
> > +}
> > +
> > +static int nvram_proc_read(struct seq_file *seq, void *offset)
> > +{
> > +	unsigned char contents[NVRAM_BYTES];
> > +	int i;
> > +
> > +	spin_lock_irq(&rtc_lock);
> > +	for (i = 0; i < NVRAM_BYTES; ++i)
> > +		contents[i] = __nvram_read_byte(i);
> > +	spin_unlock_irq(&rtc_lock);
> > +
> > +	atari_nvram_proc_read(contents, seq, offset);
> > +
> > +	return 0;
> > +}
> > +
> > +static int __init atari_nvram_init(void)
> > +{
> > +	if (!(MACH_IS_ATARI && ATARIHW_PRESENT(TT_CLK)))
> > +		return -ENODEV;
> > +
> > +	if (!proc_create_single("driver/nvram", 0, NULL, nvram_proc_read)) {
> > +		pr_err("nvram: can't create /proc/driver/nvram\n");
> > +		return -ENOMEM;
> > +	}
> > +
> > +	return 0;
> > +}
> > +device_initcall(atari_nvram_init);
> > +#endif /* CONFIG_PROC_FS */
> > diff --git a/drivers/char/nvram.c b/drivers/char/nvram.c
> > index 25264d65e716..a9d4652f9e90 100644
> > --- a/drivers/char/nvram.c
> > +++ b/drivers/char/nvram.c
> > @@ -21,13 +21,6 @@
> >   * ioctl(NVRAM_SETCKS) (doesn't change contents, just makes checksum valid
> >   * again; use with care!)
> >   *
> > - * This file also provides some functions for other parts of the kernel that
> > - * want to access the NVRAM: nvram_{read,write,check_checksum,set_checksum}.
> > - * Obviously this can be used only if this driver is always configured into
> > - * the kernel and is not a module. Since the functions are used by  
> > some Atari
> > - * drivers, this is the case on the Atari.
> > - *
> > - *
> >   * 	1.1	Cesar Barros: SMP locking fixes
> >   * 		added changelog
> >   * 	1.2	Erik Gilling: Cobalt Networks support
> > @@ -39,64 +32,6 @@
> >
> >  #include <linux/module.h>
> >  #include <linux/nvram.h>
> > -
> > -#define PC		1
> > -#define ATARI		2
> > -
> > -/* select machine configuration */
> > -#if defined(CONFIG_ATARI)
> > -#  define MACH ATARI
> > -#elif defined(__i386__) || defined(__x86_64__) || defined(__arm__)   
> > /* and ?? */
> > -#  define MACH PC
> > -#else
> > -#  error Cannot build nvram driver for this machine configuration.
> > -#endif
> > -
> > -#if MACH == PC
> > -
> > -/* RTC in a PC */
> > -#define CHECK_DRIVER_INIT()	1
> > -
> > -/* On PCs, the checksum is built only over bytes 2..31 */
> > -#define PC_CKS_RANGE_START	2
> > -#define PC_CKS_RANGE_END	31
> > -#define PC_CKS_LOC		32
> > -#define NVRAM_BYTES		(128-NVRAM_FIRST_BYTE)
> > -
> > -#define mach_check_checksum	pc_check_checksum
> > -#define mach_set_checksum	pc_set_checksum
> > -#define mach_proc_infos		pc_proc_infos
> > -
> > -#endif
> > -
> > -#if MACH == ATARI
> > -
> > -/* Special parameters for RTC in Atari machines */
> > -#include <asm/atarihw.h>
> > -#include <asm/atariints.h>
> > -#define RTC_PORT(x)		(TT_RTC_BAS + 2*(x))
> > -#define CHECK_DRIVER_INIT()	(MACH_IS_ATARI && ATARIHW_PRESENT(TT_CLK))
> > -
> > -#define NVRAM_BYTES		50
> > -
> > -/* On Ataris, the checksum is over all bytes except the checksum bytes
> > - * themselves; these are at the very end */
> > -#define ATARI_CKS_RANGE_START	0
> > -#define ATARI_CKS_RANGE_END	47
> > -#define ATARI_CKS_LOC		48
> > -
> > -#define mach_check_checksum	atari_check_checksum
> > -#define mach_set_checksum	atari_set_checksum
> > -#define mach_proc_infos		atari_proc_infos
> > -
> > -#endif
> > -
> > -/* Note that *all* calls to CMOS_READ and CMOS_WRITE must be done with
> > - * rtc_lock held. Due to the index-port/data-port design of the RTC, we
> > - * don't want two different things trying to get to it at once. (e.g. the
> > - * periodic 11 min sync from kernel/time/ntp.c vs. this driver.)
> > - */
> > -
> >  #include <linux/types.h>
> >  #include <linux/errno.h>
> >  #include <linux/miscdevice.h>
> > @@ -120,12 +55,9 @@ static int nvram_open_mode;	/* special open modes */
> >  #define NVRAM_WRITE		1 /* opened for writing (exclusive) */
> >  #define NVRAM_EXCL		2 /* opened with O_EXCL */
> >
> > -static int mach_check_checksum(void);
> > -static void mach_set_checksum(void);
> > -
> >  #ifdef CONFIG_PROC_FS
> > -static void mach_proc_infos(unsigned char *contents, struct seq_file *seq,
> > -								void *offset);
> > +static void pc_nvram_proc_read(unsigned char *contents, struct  
> > seq_file *seq,
> > +			       void *offset);
> >  #endif
> >
> >  /*
> > @@ -139,6 +71,14 @@ static void mach_proc_infos(unsigned char  
> > *contents, struct seq_file *seq,
> >   * know about the RTC cruft.
> >   */
> >
> > +#define NVRAM_BYTES		(128 - NVRAM_FIRST_BYTE)
> > +
> > +/* Note that *all* calls to CMOS_READ and CMOS_WRITE must be done with
> > + * rtc_lock held. Due to the index-port/data-port design of the RTC, we
> > + * don't want two different things trying to get to it at once. (e.g. the
> > + * periodic 11 min sync from kernel/time/ntp.c vs. this driver.)
> > + */
> > +
> >  unsigned char __nvram_read_byte(int i)
> >  {
> >  	return CMOS_READ(NVRAM_FIRST_BYTE + i);
> > @@ -174,9 +114,22 @@ void nvram_write_byte(unsigned char c, int i)
> >  }
> >  EXPORT_SYMBOL(nvram_write_byte);
> >
> > +/* On PCs, the checksum is built only over bytes 2..31 */
> > +#define PC_CKS_RANGE_START	2
> > +#define PC_CKS_RANGE_END	31
> > +#define PC_CKS_LOC		32
> > +
> >  int __nvram_check_checksum(void)
> >  {
> > -	return mach_check_checksum();
> > +	int i;
> > +	unsigned short sum = 0;
> > +	unsigned short expect;
> > +
> > +	for (i = PC_CKS_RANGE_START; i <= PC_CKS_RANGE_END; ++i)
> > +		sum += __nvram_read_byte(i);
> > +	expect = __nvram_read_byte(PC_CKS_LOC)<<8 |
> > +	    __nvram_read_byte(PC_CKS_LOC+1);
> > +	return (sum & 0xffff) == expect;
> >  }
> 
> 
> I don't understand how this is part of the code move.
> Does the pc specific checksum becomes the generic one ?
> 

This is not generic code, of course. Please refer to the two patches that 
follow this one, in which all of the x86-specific code gets wrapped with 
#ifdef CONFIG_X86.

This code gets moved because the MACH macro is made redundant. You might 
defer this code motion to patch 4 or patch 5 but I don't see that as being 
an improvement.

You may want to take a look at the final generic implementation of 
drivers/char/nvram.c, which can be seen here: 
https://github.com/fthain/linux/blob/0949c1b7bd8b9d0034e77601a9af73c712d26d4a/drivers/char/nvram.c

You may also find it helpful to look at this whole series in the form of a 
single diff, to reveal the effect on this file. I think you'll agree that 
the overall effect on this file is a dramatic improvement.

You may argue that there should be no CONFIG_X86 code in drivers/char. 
Sure, that would be nice. However, if you grep for CMOS_READ|CMOS_WRITE 
you'll see that the problem is much bigger than drivers/char/nvram.c.
Perhaps the next best place for the x86-specific code here is 
drivers/rtc/rtc-cmos.c where you can already find #ifdef CONFIG_X86. 

Anyway, I consider the CMOS_READ|CMOS_WRITE issue to be out-of-scope, 
though hopefully this patch series does untangle it a little.

--