Messages in this thread | | | Date | Wed, 7 Feb 2018 16:47:00 +0100 | From | Alexandre Belloni <> | Subject | Re: [PATCH] char: nvram: disable on ARM |
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On 07/02/2018 at 15:00:04 +0100, Arnd Bergmann wrote: > On Wed, Feb 7, 2018 at 1:48 PM, Alexandre Belloni > <alexandre.belloni@bootlin.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. >
Actually, I just found https://unix.stackexchange.com/questions/331419/is-dev-nvram-dangerous-to-write-to
So it seems to have real values for some people (even if they are wrong).
That also points to https://sourceforge.net/projects/nvram-wakeup/ but I don't think it is necessary. The RTC driver should be able to wakeup an x86 platform.
All the other uses of /dev/nvram I could find with a simple google search (i.e. saving and restoring CMOS settings) could just use /sys/class/rtc/rtc0/device/nvram
> 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. >
I guess we can do that, provided we take rtc_lock before using CMOS_READ.
Thinking of it, I think this means we don't need the lock for powerpc as nvram_read_byte doesn't take it. So I guess it is only needed on x86.
-- Alexandre Belloni, Bootlin (formerly Free Electrons) Embedded Linux and Kernel engineering http://bootlin.com
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