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

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Date:   Tue, 12 Mar 2019 17:19:32 +0800
From:   Tom Li <tomli@...li.me>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Jani Nikula <jani.nikula@...ux.intel.com>,
        Linux Fbdev development list <linux-fbdev@...r.kernel.org>,
        DRI Development <dri-devel@...ts.freedesktop.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Sudip Mukherjee <sudipm.mukherjee@...il.com>,
        Teddy Wang <teddy.wang@...iconmotion.com>
Subject: Re: Is it possible to reset graphics controller on reboot in a
 framebuffer driver?

On Fri, Mar 08, 2019 at 06:35:36PM +0800, Tom Li wrote:
> On Fri, Mar 08, 2019 at 10:13:58AM +0100, Geert Uytterhoeven wrote:
> > On Thu, Mar 7, 2019 at 10:38 PM Tom Li <tomli@...li.me> wrote:
> > > Nevertheless, does it mean there's no way to prevent it from happening if the
> > > user issues a emergency reboot? Like an automatic reboot after a kernel panic,
> > > or a SysRq-B reboot.
> > 
> > If Linux performs a reboot, it calls the shutdown handlers.
> > I think that includes reboot on panic, or SysRq-B, but I'd have to check to
> > be 100% sure.
> 
> Okay, glad to hear that. If it works for SysRq-B or panic reboot, I think
> it would be enough. After all, hard kernel crashes are rare nowadays, and
> most crashes are hard lockups. In case it happens, the user just presses
> the power button to halt.

As I suspected, emergency reboot via SysRq-B is a hard reboot and none of the
reboot handler will be called. I've put a for (;;) {} loop in .shutdown(), the
kernel would hang during a normal reboot, but a SysRq-B reboot will reset the
machine immediately.

Fortunately, I've found a way to stop trigger the bug in the driver, so no
shutdown handler is needed anymore.

Cheers,
Tom Li