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Date:   Sun, 15 Oct 2017 23:40:14 +0300
From:   Sakari Ailus <>
To:     Nicolas Dufresne <>
Cc:     Stanimir Varbanov <>,
        Mauro Carvalho Chehab <>,
        Pawel Osciak <>,
        Marek Szyprowski <>,
        Kyungmin Park <>,,
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
> 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

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

Kind regards,

Sakari Ailus

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