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

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Date:   Thu, 17 Nov 2022 19:01:05 +0100
From:   Christian König <christian.koenig@....com>
To:     Dmitry Osipenko <dmitry.osipenko@...labora.com>,
        Lukasz Wiecaszek <lukasz.wiecaszek@...glemail.com>
Cc:     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

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.