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From: "Michel Dänzer" <michel@daenzer.net>
To: "Alex Deucher" <alexdeucher@gmail.com>,
	"Christian König" <christian.koenig@amd.com>,
	"Zhenneng Li" <lizhenneng@kylinos.cn>,
	"Alex Deucher" <alexander.deucher@amd.com>,
	"Pan, Xinhui" <Xinhui.Pan@amd.com>,
	"David Airlie" <airlied@linux.ie>,
	"amd-gfx list" <amd-gfx@lists.freedesktop.org>,
	"Maling list - DRI developers" <dri-devel@lists.freedesktop.org>,
	LKML <linux-kernel@vger.kernel.org>
Cc: Daniel Vetter <daniel@ffwll.ch>
Subject: Re: [PATCH] drm/radeon: Update pitch for page flip
Date: Tue, 3 Aug 2021 10:34:06 +0200	[thread overview]
Message-ID: <6a34fcc3-0aa3-85ff-21c4-86b9b5a48fd5@daenzer.net> (raw)
In-Reply-To: <CADnq5_PDtEn1y5HJBRHXw8o11LVwSRDKNtQgZtN5u0CW5ZspnQ@mail.gmail.com>

On 2021-08-02 4:51 p.m., Alex Deucher wrote:
> On Mon, Aug 2, 2021 at 4:31 AM Daniel Vetter <daniel@ffwll.ch> wrote:
>>
>> On Mon, Aug 02, 2021 at 10:12:47AM +0200, Christian König wrote:
>>> Am 02.08.21 um 09:43 schrieb Zhenneng Li:
>>>> When primary bo is updated, crtc's pitch may
>>>> have not been updated, this will lead to show
>>>> disorder content when user changes display mode,
>>>> we update crtc's pitch in page flip to avoid
>>>> this bug.
>>>> This refers to amdgpu's pageflip.
>>>
>>> Alex is the expert to ask about that code, but I'm not sure if that is
>>> really correct for the old hardware.
>>>
>>> As far as I know the crtc's pitch should not change during a page flip, but
>>> only during a full mode set.
>>>
>>> So could you elaborate a bit more how you trigger this?
>>
>> legacy page_flip ioctl only verifies that the fb->format stays the same.
>> It doesn't check anything else (afair never has), this is all up to
>> drivers to verify.
>>
>> Personally I'd say add a check to reject this, since testing this and
>> making sure it really works everywhere is probably a bit much on this old
>> hw.
> 
> If just the pitch changed, that probably wouldn't be much of a
> problem, but if the pitch is changing, that probably implies other
> stuff has changed as well and we'll just be chasing changes.  I agree
> it would be best to just reject anything other than updating the
> scanout address.

FWIW, that means page flipping cannot be used in some cases which work fine by changing the pitch, which can result in tearing: https://gitlab.freedesktop.org/xorg/xserver/-/issues/839 (which says the i915 driver handles this as well).


-- 
Earthling Michel Dänzer               |               https://redhat.com
Libre software enthusiast             |             Mesa and X developer

  parent reply	other threads:[~2021-08-03  8:34 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-02  7:43 Zhenneng Li
     [not found] ` <e6e77cfb-4e6b-c30e-ae7c-ac84b82c9a75@amd.com>
2021-08-02  8:31   ` Daniel Vetter
2021-08-02 14:51     ` Alex Deucher
2021-08-03  8:00       ` 李真能
2021-08-03  8:34       ` Michel Dänzer [this message]
2021-08-03 14:49         ` Alex Deucher
2021-08-04 15:46           ` Daniel Vetter

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