Re: [PATCH] char: nvram: disable on ARM

On Wed, Feb 7, 2018 at 2:55 AM, Alexandre Belloni
[off-list ref] wrote:

On 06/02/2018 at 23:55:02 +0100, Arnd Bergmann wrote:

quoted

* arch/arm/kernel/time.c has this code

#if defined(CONFIG_RTC_DRV_CMOS) || defined(CONFIG_RTC_DRV_CMOS_MODULE) || \
    defined(CONFIG_NVRAM) || defined(CONFIG_NVRAM_MODULE)
/* this needs a better home */
DEFINE_SPINLOCK(rtc_lock);
EXPORT_SYMBOL(rtc_lock);
#endif  /* pc-style 'CMOS' RTC support */

That can be adapted now, or maybe we could move all definitions into
a common place (that needs some more planning).

Yes, on arm, the rtc_lock is mostly there to please
drivers/rtc/rtc-cmos.c. Maybe we could make the locking in this driver
x86 and PPC specific.

If we can get rid of arch/powerpc/platforms/chrp/time.c and
arch/powerpc/platforms/maple/time.c (so much duplicated code), then it
is x86 only.

What about these:

arch/alpha/kernel/rtc.c:        spin_lock(&rtc_lock);
arch/alpha/kernel/rtc.c:        spin_unlock(&rtc_lock);
arch/alpha/kernel/time.c:DEFINE_SPINLOCK(rtc_lock);
arch/alpha/kernel/time.c:EXPORT_SYMBOL(rtc_lock);
arch/arm/kernel/time.c:DEFINE_SPINLOCK(rtc_lock);
arch/arm/kernel/time.c:EXPORT_SYMBOL(rtc_lock);
arch/m32r/kernel/time.c:DEFINE_SPINLOCK(rtc_lock);
arch/m32r/kernel/time.c:EXPORT_SYMBOL(rtc_lock);
arch/m68k/atari/time.c:DEFINE_SPINLOCK(rtc_lock);
arch/m68k/atari/time.c:EXPORT_SYMBOL_GPL(rtc_lock);
arch/mn10300/kernel/rtc.c:DEFINE_SPINLOCK(rtc_lock);
arch/mn10300/kernel/rtc.c:EXPORT_SYMBOL(rtc_lock);
arch/powerpc/kernel/time.c:DEFINE_SPINLOCK(rtc_lock);
arch/powerpc/kernel/time.c:EXPORT_SYMBOL_GPL(rtc_lock);
arch/sparc/kernel/time_32.c:DEFINE_SPINLOCK(rtc_lock);
arch/sparc/kernel/time_32.c:EXPORT_SYMBOL(rtc_lock);
arch/sparc/kernel/time_64.c:DEFINE_SPINLOCK(rtc_lock);

Are they all obsolete?

quoted

* similarly, this line in nvram.c can be simplified:
#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

* GENERIC_NVRAM is not really generic, instead this seems to be the
  chardev that is used for 32-bit powerpc (powermac, 85xx, 86xx), while
  64-bit powerpc (cell, maple, opal, pseries) use code from
  arch/powerpc/kernel/nvram_64.c, with the same underlying arch hooks.
  The nvram_64 code appears to be mostly a superset of the 32-bit
  generic_nvram one.

* The code in drivers/char/nvram is not used at all when
   GENERIC_NVRAM is set, and half the code in there is different
   between x86 and atari.

* most of the external interface in include/linux/nvram.h is
  unused, the rest tends to be architecture specific

* The procfs file appears to be completely useless on any 64-bit
   x86 machine, this is what I see:

$ cat /proc/driver/nvram
Checksum status: valid
# floppies     : 0
Floppy 0 type  : none
Floppy 1 type  : none
HD 0 type      : none
HD 1 type      : none
HD type 48 data: 0/0/0 C/H/S, precomp 0, lz 0
HD type 49 data: 156/0/0 C/H/S, precomp 0, lz 0
DOS base memory: 635 kB
Extended memory: 65535 kB (configured), 65535 kB (tested)
Gfx adapter    : EGA, VGA, ... (with BIOS)
FPU            : not installed

I really don't think anyone is using that but I don't really know much
about x86 and the specification this may be part of.

I see the info may be used in drivers/video/fbdev/ and
drivers/platform/x86/thinkpad_acpi.c

The thinkpad_acpi driver seems to look at some other bytes
in the nvram, which have a platform specific meaning.

For drivers/video/fbdev/, these appear to all be for pre-x86
Apple Macintosh (m68k or powerpc).

       Arnd