linux-kernel - Re: [PATCH 4.18 74/88] drm/atomic: Use drm_drv_uses_atomic

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Date:   Thu, 27 Sep 2018 16:18:26 +0200
From:   Holger Hoffstätte <holger@...lied-asynchrony.com>
To:     Sean Paul <sean@...rly.run>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Lyude Paul <lyude@...hat.com>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Sean Paul <seanpaul@...omium.org>
Subject: Re: [PATCH 4.18 74/88] drm/atomic: Use drm_drv_uses_atomic_modeset()
 for debugfs creation

On 09/27/18 16:05, Sean Paul wrote:
> On Thu, Sep 27, 2018 at 03:53:26PM +0200, Holger Hoffstätte wrote:
>> On 09/27/18 15:26, Holger Hoffstätte wrote:
>>> On 09/27/18 14:37, Greg Kroah-Hartman wrote:
>>>> On Thu, Sep 27, 2018 at 12:43:33PM +0200, Holger Hoffstätte wrote:
>>>>> On 09/27/18 11:03, Greg Kroah-Hartman wrote:
>>>>>> 4.18-stable review patch.  If anyone has any objections, please let me know.
>>>>>>
>>>>>> ------------------
>>>>>>
>>>>>> From: Lyude Paul <lyude@...hat.com>
>>>>>>
>>>>>> commit 3c499ea0c662e2f38aafbd4f516b08aab8cfa0e5 upstream.
>>>>>>
>>>>>> As pointed out by Daniel Vetter, we should be usinng
>>>>>> drm_drv_uses_atomic_modeset() for determining whether or not we want to
>>>>>> make the debugfs nodes for atomic instead of checking DRIVER_ATOMIC, as
>>>>>> the former isn't an accurate representation of whether or not the driver
>>>>>> is actually using atomic modesetting internally (even though it might
>>>>>> not be exposing atomic capabilities).
>>>>>>
>>>>>> Signed-off-by: Lyude Paul <lyude@...hat.com>
>>>>>> Cc: Daniel Vetter <daniel.vetter@...ll.ch>
>>>>>> Cc: stable@...r.kernel.org
>>>>>> Reviewed-by: Sean Paul <seanpaul@...omium.org>
>>>>>> Link: https://patchwork.freedesktop.org/patch/msgid/20180917173733.21293-1-lyude@redhat.com
>>>>>> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
>>>>>
>>>>> This patch breaks switching the console to high resolution during boot on my
>>>>> workstation with a Radeon card; it worked fine with 4.18.10 and reverting it
>>>>> fixes the problem:
>>>>
>>>> Is 4.19-rc5 also a problem?
>>>>
>>>
>>> No, 4.19-rc5 with the same config works fine and properly switches the
>>> console during boot.
>>>
>>> Interestingly another machine with i915 chip seemed to work fine with this
>>> patch included (rebooted that one first), so it might well be related to
>>> different motherboard/chipset or the Radeon card (an admittedly old, but
>>> otherwise completely functional fanless r600).
>>>
>>> I'll try to find more clues, but for now that's all I got.
>>
>> Looking at mainline include/drm I see several recent movements and cleanups
>> related to drm_drv_uses_atomic_modeset(), moving it out of drmP.h and into
>> drm, changes to atomic modesetting and such, all part of the 4.19 merge
>> window. I'm reasonably sure some relatred changes went missing here wrt.
>> this patch.
> 
> Hey all,
> Thanks for testing, Holger.
> 
> This was fixed with https://patchwork.freedesktop.org/patch/250350/ which is not
> Cc stable.

That's what I just looked at, it's in mainline as well. I briefly considered
backporting that fix manually, but was not sure why radeon is apparently not
a "modesetting driver" and figured I'd rather wait for someone who understands
drm better than me.

> I think it'd be best to just drop the initial patch from stable, it
> doesn't need to go back afaict.

Agreed - using 4.18.11 just fine right now without it. :)

cheers,
Holger