linux-kernel - Re: [PATCH v4] udmabuf: add vmap and vunmap methods to udmabuf

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Date:   Fri, 18 Nov 2022 10:42:42 +0100
From:   Lukasz Wiecaszek <lukasz.wiecaszek@...glemail.com>
To:     Christian König <christian.koenig@....com>
Cc:     Dmitry Osipenko <dmitry.osipenko@...labora.com>,
        Lukasz Wiecaszek <lukasz.wiecaszek@...glemail.com>,
        Gerd Hoffmann <kraxel@...hat.com>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        dri-devel@...ts.freedesktop.org, linux-media@...r.kernel.org,
        linaro-mm-sig@...ts.linaro.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] udmabuf: add vmap and vunmap methods to udmabuf_ops

On Thu, Nov 17, 2022 at 07:01:05PM +0100, Christian König wrote:
> Am 17.11.22 um 18:32 schrieb Dmitry Osipenko:
> > On 11/17/22 20:08, Lukasz Wiecaszek wrote:
> > > On Thu, Nov 17, 2022 at 12:04:35PM +0300, Dmitry Osipenko wrote:
> > > > Hi,
> > > > 
> > > > On 11/17/22 07:58, Lukasz Wiecaszek wrote:
> > > > > The reason behind that patch is associated with videobuf2 subsystem
> > > > > (or more genrally with v4l2 framework) and user created
> > > > > dma buffers (udmabuf). In some circumstances
> > > > > when dealing with V4L2_MEMORY_DMABUF buffers videobuf2 subsystem
> > > > > wants to use dma_buf_vmap() method on the attached dma buffer.
> > > > > As udmabuf does not have .vmap operation implemented,
> > > > > such dma_buf_vmap() natually fails.
> > > > > 
> > > > > videobuf2_common: __vb2_queue_alloc: allocated 3 buffers, 1 plane(s) each
> > > > > videobuf2_common: __prepare_dmabuf: buffer for plane 0 changed
> > > > > videobuf2_common: __prepare_dmabuf: failed to map dmabuf for plane 0
> > > > > videobuf2_common: __buf_prepare: buffer preparation failed: -14
> > > > > 
> > > > > The patch itself seems to be strighforward.
> > > > > It adds implementation of .vmap and .vunmap methods
> > > > > to 'struct dma_buf_ops udmabuf_ops'.
> > > > > .vmap method itself uses vm_map_ram() to map pages linearly
> > > > > into the kernel virtual address space.
> > > > > .vunmap removes mapping created earlier by .vmap.
> > > > > All locking and 'vmapping counting' is done in dma_buf.c
> > > > > so it seems to be redundant/unnecessary in .vmap/.vunmap.
> > > > > 
> > > > > Signed-off-by: Lukasz Wiecaszek <lukasz.wiecaszek@...il.com>
> > > > If new patch version doesn't contain significant changes and you got
> > > > acks/reviews for the previous version, then you should add the given
> > > > acked-by and reviewed-by tags to the commit message by yourself.
> > > > 
> > > > -- 
> > > > Best regards,
> > > > Dmitry
> > > > 
> > > I would like to thank you all for your patience and on the same time say
> > > sorry that I still cannot follow the process (although I have read
> > > 'submitting patches' chapter).
> > If you'll continue to contribute actively, you'll find things that
> > aren't documented at all. Don't worry about it, usually somebody will
> > tell you about what's missing. Just apply the new knowledge next time ;)
> 
> Yeah, it's more learning by doing. Especially I suspect you don't have
> commit rights to drm-misc-next (or do you want to upstream it through some
> other branch?), so as soon as nobody has any more objections ping Dmitry or
> me to push this.
> 
> Cheers,
> Christian
> 
> PS: The Signed-of-by, Reviewed-by, Acked-by etc... lines are usually added
> in chronological order, e.g. your Signed-of-by line should always come
> first.
> 
>
Thanks one more time. Funny thing, but at the very beginning I had
Signed-of-by as the first line. Then I looked at 'git log' and spoted
different order, so I change mine as well. Ahhh. But this chronological
order of course make sense. So if you feel ok with this 'out of order'
issue, please push/merge this commit. If not, please let me know. I
already submitted version 5 of that work. So if change is required, I
will prepare version 6.