linux-kernel - Re: [PATCH 2/8] fbdev: sm712fb: fix brightness control on reboot, don't set SR30.

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Message-ID: <20190331121907.npu4kehmgxmmf44j@debian>
Date:   Sun, 31 Mar 2019 13:19:07 +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 2/8] fbdev: sm712fb: fix brightness control on reboot,
 don't set SR30.

On Sun, Mar 17, 2019 at 06:24:58AM +0800, Yifeng Li wrote:
> On a Thinkpad s30 (Pentium III / i440MX, Lynx3DM), rebooting with
> sm712fb framebuffer driver would cause the role of brightness up/down
> button to swap.
> 
> Experiments showed the FPR30 register caused this behavior. Moreover,
> even if this register don't have side-effect on other systems, over-
> writing it is also highly questionable, since it was originally
> configurated by the motherboard manufacturer by hardwiring pull-down
> resistors to indicate the type of LCD panel. We should not mess with
> it.
> 
> Stop writing to the SR30 (a.k.a FPR30) register.
> 
> 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