linux-kernel - Re: [PATCH] media: vb2: unify calling of set_page_dirty

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Message-ID: <20171015204014.2awhhygw6hi3lxas@valkosipuli.retiisi.org.uk>
Date:   Sun, 15 Oct 2017 23:40:14 +0300
From:   Sakari Ailus <sakari.ailus@....fi>
To:     Nicolas Dufresne <nicolas@...fresne.ca>
Cc:     Stanimir Varbanov <stanimir.varbanov@...aro.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Pawel Osciak <pawel@...iak.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] media: vb2: unify calling of set_page_dirty_lock

Hi Nicolas,

On Tue, Oct 10, 2017 at 11:40:10AM -0400, Nicolas Dufresne wrote:
> Le mardi 29 août 2017 à 14:26 +0300, Stanimir Varbanov a écrit :
> > Currently videobuf2-dma-sg checks for dma direction for
> > every single page and videobuf2-dc lacks any dma direction
> > checks and calls set_page_dirty_lock unconditionally.
> > 
> > Thus unify and align the invocations of set_page_dirty_lock
> > for videobuf2-dc, videobuf2-sg  memory allocators with
> > videobuf2-vmalloc, i.e. the pattern used in vmalloc has been
> > copied to dc and dma-sg.
> 
> Just before we go too far in "doing like vmalloc", I would like to
> share this small video that display coherency issues when rendering
> vmalloc backed DMABuf over various KMS/DRM driver. I can reproduce this
> easily with Intel and MSM display drivers using UVC or Vivid as source.
> 
> The following is an HDMI capture of the following GStreamer pipeline
> running on Dragonboard 410c.
> 
>     gst-launch-1.0 -v v4l2src device=/dev/video2 ! video/x-raw,format=NV16,width=1280,height=720 ! kmssink
>     https://people.collabora.com/~nicolas/vmalloc-issue.mov
> 
> Feedback on this issue would be more then welcome. It's not clear to me
> who's bug is this (v4l2, drm or iommu). The software is unlikely to be
> blamed as this same pipeline works fine with non-vmalloc based sources.

Could you elaborate this a little bit more? Which Intel CPU do you have
there?

Where are the buffers allocated for this GStreamer pipeline, is it v4l2src
or another element or somewhere else?

-- 
Kind regards,

Sakari Ailus
e-mail: sakari.ailus@....fi