linux-kernel - Re: [PATCH 3/8] fbdev: sm712fb: fix VRAM detection, don't set SR70/71/74/75.

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Message-ID: <20190331121924.5wjhhjp2j2gom7zp@debian>
Date:   Sun, 31 Mar 2019 13:19:24 +0100
From:   Sudip Mukherjee <sudipm.mukherjee@...il.com>
To:     Yifeng Li <tomli@...li.me>
Cc:     Teddy Wang <teddy.wang@...iconmotion.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        linux-fbdev@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH 3/8] fbdev: sm712fb: fix VRAM detection, don't set
 SR70/71/74/75.

On Sun, Mar 17, 2019 at 06:24:59AM +0800, Yifeng Li wrote:
> On a Thinkpad s30 (Pentium III / i440MX, Lynx3DM), the amount of Video
> RAM is not detected correctly by the xf86-video-siliconmotion driver.
> This is because sm712fb overwrites the GPR71 Scratch Pad Register, which
> is set by BIOS on x86 and used to indicate amount of VRAM.
> 
> Other Scratch Pad Registers, including GPR70/74/75, don't have the same
> side-effect, but overwriting to them is still questionable, as they are
> not related to modesetting.
> 
> Stop writing to SR70/71/74/75 (a.k.a GPR70/71/74/75).
> 
> Signed-off-by: Yifeng Li <tomli@...li.me>
> Cc: stable@...r.kernel.org  # v4.4+

Tested-by: Sudip Mukherjee <sudipm.mukherjee@...il.com>

--
Regards
Sudip