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

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Date:   Thu, 17 Nov 2022 18:08:38 +0100
From:   Lukasz Wiecaszek <lukasz.wiecaszek@...glemail.com>
To:     Dmitry Osipenko <dmitry.osipenko@...labora.com>
Cc:     Lukasz Wiecaszek <lukasz.wiecaszek@...glemail.com>,
        Gerd Hoffmann <kraxel@...hat.com>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Christian König <christian.koenig@....com>,
        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 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).