linux-kernel - Re: [PATCH v3] udmabuf: add vmap and vunmap methods to udmabuf

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Message-ID: <4f92e95f-a0dc-4eac-4c08-0df85de78ae7@collabora.com>
Date:   Wed, 16 Nov 2022 15:18:31 +0300
From:   Dmitry Osipenko <dmitry.osipenko@...labora.com>
To:     Lukasz Wiecaszek <lukasz.wiecaszek@...glemail.com>,
        Gerd Hoffmann <kraxel@...hat.com>
Cc:     Lukasz Wiecaszek <lukasz.wiecaszek@...il.com>,
        kernel test robot <lkp@...el.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 v3] udmabuf: add vmap and vunmap methods to udmabuf_ops

On 11/15/22 23:04, 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>
> Reported-by: kernel test robot <lkp@...el.com>
> ---
> v1: https://lore.kernel.org/linux-media/202211120352.G7WPASoP-lkp@intel.com/T/#t
> v2: https://lore.kernel.org/linux-media/20221114052944.GA7264@thinkpad-p72/T/#t
> 
> v2 -> v3: Added .vunmap to 'struct dma_buf_ops udmabuf_ops'
> v1 -> v2: Patch prepared and tested against 6.1.0-rc2+
> 
>  drivers/dma-buf/udmabuf.c | 28 ++++++++++++++++++++++++++++
>  1 file changed, 28 insertions(+)
> 
> diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
> index 283816fbd72f..740d6e426ee9 100644
> --- a/drivers/dma-buf/udmabuf.c
> +++ b/drivers/dma-buf/udmabuf.c
> @@ -13,6 +13,8 @@
>  #include <linux/slab.h>
>  #include <linux/udmabuf.h>
>  #include <linux/hugetlb.h>
> +#include <linux/vmalloc.h>
> +#include <linux/iosys-map.h>
>  
>  static int list_limit = 1024;
>  module_param(list_limit, int, 0644);
> @@ -60,6 +62,30 @@ static int mmap_udmabuf(struct dma_buf *buf, struct vm_area_struct *vma)
>  	return 0;
>  }
>  
> +static int vmap_udmabuf(struct dma_buf *buf, struct iosys_map *map)
> +{
> +	struct udmabuf *ubuf = buf->priv;
> +	void *vaddr;
> +
> +	dma_resv_assert_held(buf->resv);
> +
> +	vaddr = vm_map_ram(ubuf->pages, ubuf->pagecount, -1);
> +	if (!vaddr)
> +		return -EINVAL;
> +
> +	iosys_map_set_vaddr(map, vaddr);
> +	return 0;
> +}
> +
> +static void vunmap_udmabuf(struct dma_buf *buf, struct iosys_map *map)
> +{
> +	struct udmabuf *ubuf = buf->priv;
> +
> +	dma_resv_assert_held(buf->resv);
> +
> +	vm_unmap_ram(map->vaddr, ubuf->pagecount);
> +}
> +
>  static struct sg_table *get_sg_table(struct device *dev, struct dma_buf *buf,
>  				     enum dma_data_direction direction)
>  {
> @@ -162,6 +188,8 @@ static const struct dma_buf_ops udmabuf_ops = {
>  	.unmap_dma_buf	   = unmap_udmabuf,
>  	.release	   = release_udmabuf,
>  	.mmap		   = mmap_udmabuf,
> +	.vmap		   = vmap_udmabuf,
> +	.vunmap		   = vunmap_udmabuf,
>  	.begin_cpu_access  = begin_cpu_udmabuf,
>  	.end_cpu_access    = end_cpu_udmabuf,
>  };

Reviewed-by: Dmitry Osipenko <dmitry.osipenko@...labora.com>

-- 
Best regards,
Dmitry