linux-kernel - Re: Is it possible to reset graphics controller on reboot in a framebuffer driver?

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Date:   Thu, 07 Mar 2019 11:00:49 +0200
From:   Jani Nikula <jani.nikula@...ux.intel.com>
To:     Tom Li <tomli@...li.me>, linux-fbdev@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Cc:     Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Sudip Mukherjee <sudipm.mukherjee@...il.com>,
        Yifeng Li <tomli@...li.me>,
        Teddy Wang <teddy.wang@...iconmotion.com>
Subject: Re: Is it possible to reset graphics controller on reboot in a framebuffer driver?

On Thu, 07 Mar 2019, Tom Li <tomli@...li.me> wrote:
> Hi all.
>
> As you may have noticed, recently I've been working on a reworked version
> of sm712fb, and planned to convert it to a DRM/KMS driver. Besides using
> it on embedded/non-x86 systems, I thought it would be a good idea to support
> histrocial x86 laptops with this VGA chipset as well, so I've acquired a
> machine for testing.
>
> However, soon I found a nasty problem. The BIOS does not reset the chip
> on boot! Like most graphics controller of that era, sm712 chipset has a
> VGA compatible mode and a 2D framebuffer mode. The power-on default is
> VGA. The BIOS writer just assumed this, and does nothing to reinitialize
> it. If one uses the framebuffer driver under Linux, once the machine reboots,
> the entire LCD panel becomes a piece of garbage.
>
> AFAIK, the framebuffer driver would be running throughout the kernel's life-
> cycle, is it really possible to workaround this issue by restoring on VGA
> state upon reboot?

It's possible to do this using a reboot notifier. I am not sure if there
are better ways to achieve the same, but there's at least one example of
using reboot notifiers to achieve the exact same goal.

See drivers/video/fbdev/aty/atyfb_base.c, look for
register_reboot_notifier().


HTH,
Jani.

-- 
Jani Nikula, Intel Open Source Graphics Center