linux-kernel - Re: [PATCH 0/4] drm/atmel-hlcdc: fix plane clipping/rotation issues

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Date:   Thu, 31 Jan 2019 13:13:22 +0000
From:   Peter Rosin <peda@...ntia.se>
To:     Boris Brezillon <bbrezillon@...nel.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        David Airlie <airlied@...ux.ie>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        Boris Brezillon <boris.brezillon@...tlin.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Nicolas Ferre <nicolas.ferre@...rochip.com>
Subject: Re: [PATCH 0/4] drm/atmel-hlcdc: fix plane clipping/rotation issues

On 2019-01-27 09:27, Boris Brezillon wrote:
> On Thu, 10 Jan 2019 15:10:28 +0000
> Peter Rosin <peda@...ntia.se> wrote:
> 
>> Hi!
>>
>> I found an unfortunate issue while recoding plane handling to use
>> drm_atomic_helper_check_plane_state(). The driver rotates clockwise,
>> which is not correct. I simply fixed it (patch 1/4), but maybe that
>> will cause regressions for unsuspecting users who simply assumed
>> that the clockwise rotation was correct? I don't know what to do
>> about that? Adding an option to get the old broken behavior seems
>> useless, wouldn't it be just as easy to just fix whatever app to
>> rotate the other way instead of adding an option somewhere?
>>
>> I have only tested this series on sama5d3, but I did check the docs
>> for various other chips (sama5d2, sama5d4, sam9n12, sam9g15, sam9g35
>> and sam9x35) supported by the driver (relevant to patch 4/4).
>>
>> Cheers,
>> Peter
>>
>> Peter Rosin (4):
>>   drm/atmel-hlcdc: rotate planes counterclockwise
>>   drm/atmel-hlcdc: do not swap w/h of the crtc when a plane is rotated
>>   drm/atmel-hlcdc: fix clipping of planes
> 
> Queued patches 1-3 to drm-misc-next.

Great, thanks.

>>   drm/atmel-hlcdc: do not immediately disable planes, wait for next
>>     frame
> 
> Still waiting for Nicolas feedback on this one.

[Adding back Nicolas, he seems to have gone missing from the list
recipients.]

I have done some testing of that patch and for me it's a definite
improvement. The test I did was removing a white plane from a white
background. Without the patch, the driver will output black where
the plane was for the current frame (since the driver does that
disc-area thing for the largest hidden part of the background).
With the patch, I get no visual glitches when removing a plane.

I use a plane to scroll a text, and if you know what to look for,
the black rectangle that flickers by as the plane with the scrolling
text is removed is little bit disturbing. Not a significant problem,
and maybe only geeks notice it, but still...

Just wanted to say that the resulting "black hole" mentioned in the
other thread really does exist and that the patch may make sense
beyond the fact that it removes usage of undocumented features.

I have not seen any bad side effects fro the patch, but admittedly
my testing was very limited and I did not try to remove the plane
while doing other stuff with the driver. So, there might still be
reasons for removing planes immediately...

Cheers,
Peter