From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.free-electrons.com (mail.free-electrons.com [62.4.15.54]) by lists.ozlabs.org (Postfix) with ESMTP id 3zc5LD0gcYzF14f for ; Thu, 8 Feb 2018 02:47:15 +1100 (AEDT) Date: Wed, 7 Feb 2018 16:47:00 +0100 From: Alexandre Belloni To: Arnd Bergmann Cc: Greg Kroah-Hartman , Linux Kernel Mailing List , linuxppc-dev Subject: Re: [PATCH] char: nvram: disable on ARM Message-ID: <20180207154700.GY3404@piout.net> References: <20180206220534.9929-1-alexandre.belloni@bootlin.com> <20180207015509.GV3404@piout.net> <20180207124839.GX3404@piout.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On 07/02/2018 at 15:00:04 +0100, Arnd Bergmann wrote: > On Wed, Feb 7, 2018 at 1:48 PM, Alexandre Belloni > 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