linux-kernel - Re: [PATCH] hwmon: (dell-smm-hwmon) Disable BIOS fan control on SET

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Date:   Thu, 14 Nov 2019 22:51:54 +0100
From:   Pali Rohár <pali.rohar@...il.com>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     Giovanni Mascellani <gio@...ian.org>,
        Jean Delvare <jdelvare@...e.com>, linux-hwmon@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] hwmon: (dell-smm-hwmon) Disable BIOS fan control on
 SET_FAN

On Thursday 14 November 2019 13:39:01 Guenter Roeck wrote:
> I can see two possibilities: Either add a pwm1_enable attribute to
> be able to set manual/automatic fan control,

I already proposed such patch in past:
https://patchwork.kernel.org/patch/9130921/

> > @@ -43,6 +49,8 @@
> >  #define I8K_SMM_GET_TEMP_TYPE	0x11a3
> >  #define I8K_SMM_GET_DELL_SIG1	0xfea3
> >  #define I8K_SMM_GET_DELL_SIG2	0xffa3
> > +#define I8K_SMM_DISABLE_BIOS	0x30a3
> > +#define I8K_SMM_ENABLE_BIOS	0x31a3

This is model or BIOS specific. For example on E6440 are used 0x34a3 /
0x35a3 SMM calls. Because of these platform specific problems we have
never incorporated this patch into mainline kernel.

Also note that userspace can issue those SMM commands on its own (via
sys_iopl or sys_ioperm), fully bypassing such "protection" proposed in
this new patch.

-- 
Pali Rohár
pali.rohar@...il.com

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