linux-kernel - Re: [PATCH v3 0/5] Fix some race conditions that exists between fbmem and sysfb

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Message-ID: <97339148-9876-cfc1-8df8-dbb21a9c3c7c@redhat.com>
Date:   Fri, 29 Apr 2022 10:06:52 +0200
From:   Javier Martinez Canillas <javierm@...hat.com>
To:     Thomas Zimmermann <tzimmermann@...e.de>,
        linux-kernel@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        dri-devel@...ts.freedesktop.org,
        Alex Deucher <alexander.deucher@....com>,
        Borislav Petkov <bp@...e.de>,
        Changcheng Deng <deng.changcheng@....com.cn>,
        Hans de Goede <hdegoede@...hat.com>,
        Helge Deller <deller@....de>, Johan Hovold <johan@...nel.org>,
        Jonathan Corbet <corbet@....net>,
        Miaoqian Lin <linmq006@...il.com>,
        Peter Jones <pjones@...hat.com>,
        Sam Ravnborg <sam@...nborg.org>,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        Yizhuo Zhai <yzhai003@....edu>,
        Zhen Lei <thunder.leizhen@...wei.com>,
        linux-doc@...r.kernel.org, linux-fbdev@...r.kernel.org
Subject: Re: [PATCH v3 0/5] Fix some race conditions that exists between fbmem
 and sysfb

Hello Daniel,

On 4/29/22 09:47, Daniel Vetter wrote:

[snip]

>>
>> Exactly, should be done when the device is registered rather than when
>> the driver is registered or a call is made to remove the conflicting FB.
>>
>> I'll rework this series with only the bits for sysfb_disable() and drop
>> the rest. We can go back to the discussion of the remaining parts later
>> if that makes sense (I still think that patch 3/5 is a better approach,
>> but let's defer that for a different series).
> 
> We need to kill sysfb _before_ the driver loads, otherwise you can have
> two drivers fighting over each another. And yes that means you might end
> up with black screen if the driver load goes wrong, but the two drivers
> fighting over each another can also result in black screens. And the
> latter isn't fixable any other way (in general at least) than by making
> sure the fw stuff is gone before driver load starts in earnest.

Yes, you are correct. I didn't realize all the possible cases when agreed
with Thomas about doing this but tried and found that it's not enough.

I've a full patch-set now and will post as a RFC so we can discuss more.

> -Daniel

-- 
Best regards,

Javier Martinez Canillas
Linux Engineering
Red Hat