linux-kernel - Re: [PATCH v5 3/7] fbdev: Restart conflicting fb removal loop when unregistering devices

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Message-ID: <4727ce99-7107-d806-cbea-cd45c6ce6106@redhat.com>
Date:   Wed, 11 May 2022 13:57:49 +0200
From:   Javier Martinez Canillas <javierm@...hat.com>
To:     Thomas Zimmermann <tzimmermann@...e.de>,
        linux-kernel@...r.kernel.org
Cc:     dri-devel@...ts.freedesktop.org, linux-fbdev@...r.kernel.org,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Helge Deller <deller@....de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH v5 3/7] fbdev: Restart conflicting fb removal loop when
 unregistering devices

Hello Thomas,

On 5/11/22 13:47, Thomas Zimmermann wrote:
> Hi Javier
> 
> Am 11.05.22 um 13:30 schrieb Javier Martinez Canillas:
>> Drivers that want to remove registered conflicting framebuffers prior to
>> register their own framebuffer, calls remove_conflicting_framebuffers().
>>
>> This function takes the registration_lock mutex, to prevent a races when
>> drivers register framebuffer devices. But if a conflicting framebuffer
>> device is found, the underlaying platform device is unregistered and this
>> will lead to the platform driver .remove callback to be called, which in
>> turn will call to the unregister_framebuffer() that takes the same lock.
>>
>> To prevent this, a struct fb_info.forced_out field was used as indication
>> to unregister_framebuffer() whether the mutex has to be grabbed or not.
>>
>> A cleaner solution is to drop the lock before platform_device_unregister()
>> so unregister_framebuffer() can take it when called from the fbdev driver,
>> and just grab the lock again after the device has been registered and do
>> a removal loop restart.
>>
>> Since the framebuffer devices will already be removed, the loop would just
>> finish when no more conflicting framebuffers are found.
>>
>> Suggested-by: Daniel Vetter <daniel.vetter@...ll.ch>
>> Signed-off-by: Javier Martinez Canillas <javierm@...hat.com>
>> Reviewed-by: Daniel Vetter <daniel.vetter@...ll.ch>
> 
> I'd like to shrink this patchset. This looks like it can be merged 

Same. At least this version dropped a few patches that we had in v4
(related to DRM_FIRMWARE capability flag).

> immediately?
>

Yes, this one is independent of the others and could be merged already.

> Best regards
> Thomas
> 

-- 
Best regards,

Javier Martinez Canillas
Linux Engineering
Red Hat