linux-kernel - Re: [PATCH] char: nvram: disable on ARM

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Date:   Wed, 7 Feb 2018 15:00:04 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Alexandre Belloni <alexandre.belloni@...tlin.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH] char: nvram: disable on ARM

On Wed, Feb 7, 2018 at 1:48 PM, Alexandre Belloni
<alexandre.belloni@...tlin.com> wrote:
> On 07/02/2018 at 11:33:55 +0100, Arnd Bergmann wrote:
>> On Wed, Feb 7, 2018 at 2:55 AM, Alexandre Belloni

>> >> $ 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.
>>
>
> Yeah, I was more concerned that they need drivers/char/nvram.c for
> nvram_read_byte so we can't simply remove the driver.

Ok, so the procfs interface may be obsolete, but we still need an
interface into the CMOS NVRAM data.

I see that the x86 version of nvram_read_byte is just a wrapper
around CMOS_READ(14 + addr). We also have some drivers
that call the low-level function directly:

arch/x86/include/asm/floppy.h:  val = CMOS_READ(0x10) & 15;
arch/x86/kernel/bootflag.c:     v = CMOS_READ(sbf_port);
drivers/char/mwave/smapi.c:     usSmapiID = CMOS_READ(0x7C);
drivers/input/misc/wistron_btns.c:              qlen = CMOS_READ(cmos_address);

I suppose we could make the thinkpad driver do the same,
or provide a 'static inline' version of nvram_read_byte somewhere.

      Arnd