[RFC,03/15] videobuf2: add V4L2_FLAG_MEMORY_NON_CONSISTENT flag
diff mbox series

Message ID 20191217032034.54897-4-senozhatsky@chromium.org
State New
Headers show
Series
  • Implement V4L2_BUF_FLAG_NO_CACHE_* flags
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Commit Message

Sergey Senozhatsky Dec. 17, 2019, 3:20 a.m. UTC
By setting or clearing V4L2_FLAG_MEMORY_NON_CONSISTENT flag
user-space should be able to set or clear queue's NON_CONSISTENT
->dma_attrs. Queue's ->dma_attrs are passed to the underlying
allocator in __vb2_buf_mem_alloc(), so user-space will be able
to request consistent or non-consistent memory allocations.

Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
---
 Documentation/media/uapi/v4l/buffer.rst | 19 +++++++++++++++++++
 include/uapi/linux/videodev2.h          |  2 ++
 2 files changed, 21 insertions(+)

Comments

Hans Verkuil Jan. 10, 2020, 9:36 a.m. UTC | #1
On 12/17/19 4:20 AM, Sergey Senozhatsky wrote:
> By setting or clearing V4L2_FLAG_MEMORY_NON_CONSISTENT flag
> user-space should be able to set or clear queue's NON_CONSISTENT
> ->dma_attrs. Queue's ->dma_attrs are passed to the underlying
> allocator in __vb2_buf_mem_alloc(), so user-space will be able
> to request consistent or non-consistent memory allocations.
> 
> Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
> ---
>  Documentation/media/uapi/v4l/buffer.rst | 19 +++++++++++++++++++
>  include/uapi/linux/videodev2.h          |  2 ++
>  2 files changed, 21 insertions(+)
> 
> diff --git a/Documentation/media/uapi/v4l/buffer.rst b/Documentation/media/uapi/v4l/buffer.rst
> index 9149b57728e5..b08b5609f5f3 100644
> --- a/Documentation/media/uapi/v4l/buffer.rst
> +++ b/Documentation/media/uapi/v4l/buffer.rst
> @@ -705,6 +705,25 @@ Buffer Flags
>  
>  .. c:type:: v4l2_memory
>  
> +Memory Consistency Flags
> +========================
> +
> +.. tabularcolumns:: |p{7.0cm}|p{2.2cm}|p{8.3cm}|
> +
> +.. cssclass:: longtable
> +
> +.. flat-table::
> +    :header-rows:  0
> +    :stub-columns: 0
> +    :widths:       3 1 4
> +
> +    * .. _`V4L2_FLAG_MEMORY_NON_CONSISTENT`:
> +
> +      - ``V4L2_FLAG_MEMORY_NON_CONSISTENT``
> +      - 0x00000001
> +      - Set DMA_ATTR_NON_CONSISTENT queue memory consistency bit,
> +	so all queue buffers may be allocated in non-consistent memory.

This needs much more extensive documentation. This is a userspace API,
and it shouldn't refer to a kernelspace API. Instead, explain what it
means from a user perspective. Also, how does this relate to the cache
buffer flags?

These things are tricky, so it is worth spending some time on writing
good documentation.

Regards,

	Hans

> +
>  enum v4l2_memory
>  ================
>  
> diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h
> index 04481c717fee..d352997f2b62 100644
> --- a/include/uapi/linux/videodev2.h
> +++ b/include/uapi/linux/videodev2.h
> @@ -189,6 +189,8 @@ enum v4l2_memory {
>  	V4L2_MEMORY_DMABUF           = 4,
>  };
>  
> +#define V4L2_FLAG_MEMORY_NON_CONSISTENT		(1 << 0)
> +
>  /* see also http://vektor.theorem.ca/graphics/ycbcr/ */
>  enum v4l2_colorspace {
>  	/*
>
Sergey Senozhatsky Jan. 10, 2020, 9:46 a.m. UTC | #2
On (20/01/10 10:36), Hans Verkuil wrote:
[..]
> > diff --git a/Documentation/media/uapi/v4l/buffer.rst b/Documentation/media/uapi/v4l/buffer.rst
> > index 9149b57728e5..b08b5609f5f3 100644
> > --- a/Documentation/media/uapi/v4l/buffer.rst
> > +++ b/Documentation/media/uapi/v4l/buffer.rst
> > @@ -705,6 +705,25 @@ Buffer Flags
> >  
> >  .. c:type:: v4l2_memory
> >  
> > +Memory Consistency Flags
> > +========================
> > +
> > +.. tabularcolumns:: |p{7.0cm}|p{2.2cm}|p{8.3cm}|
> > +
> > +.. cssclass:: longtable
> > +
> > +.. flat-table::
> > +    :header-rows:  0
> > +    :stub-columns: 0
> > +    :widths:       3 1 4
> > +
> > +    * .. _`V4L2_FLAG_MEMORY_NON_CONSISTENT`:
> > +
> > +      - ``V4L2_FLAG_MEMORY_NON_CONSISTENT``
> > +      - 0x00000001
> > +      - Set DMA_ATTR_NON_CONSISTENT queue memory consistency bit,
> > +	so all queue buffers may be allocated in non-consistent memory.
> 
> This needs much more extensive documentation. This is a userspace API,
> and it shouldn't refer to a kernelspace API. Instead, explain what it
> means from a user perspective. Also, how does this relate to the cache
> buffer flags?
> 
> These things are tricky, so it is worth spending some time on writing
> good documentation.

Agreed. I'll give it a shot, will try to improve it.

	-ss

Patch
diff mbox series

diff --git a/Documentation/media/uapi/v4l/buffer.rst b/Documentation/media/uapi/v4l/buffer.rst
index 9149b57728e5..b08b5609f5f3 100644
--- a/Documentation/media/uapi/v4l/buffer.rst
+++ b/Documentation/media/uapi/v4l/buffer.rst
@@ -705,6 +705,25 @@  Buffer Flags
 
 .. c:type:: v4l2_memory
 
+Memory Consistency Flags
+========================
+
+.. tabularcolumns:: |p{7.0cm}|p{2.2cm}|p{8.3cm}|
+
+.. cssclass:: longtable
+
+.. flat-table::
+    :header-rows:  0
+    :stub-columns: 0
+    :widths:       3 1 4
+
+    * .. _`V4L2_FLAG_MEMORY_NON_CONSISTENT`:
+
+      - ``V4L2_FLAG_MEMORY_NON_CONSISTENT``
+      - 0x00000001
+      - Set DMA_ATTR_NON_CONSISTENT queue memory consistency bit,
+	so all queue buffers may be allocated in non-consistent memory.
+
 enum v4l2_memory
 ================
 
diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h
index 04481c717fee..d352997f2b62 100644
--- a/include/uapi/linux/videodev2.h
+++ b/include/uapi/linux/videodev2.h
@@ -189,6 +189,8 @@  enum v4l2_memory {
 	V4L2_MEMORY_DMABUF           = 4,
 };
 
+#define V4L2_FLAG_MEMORY_NON_CONSISTENT		(1 << 0)
+
 /* see also http://vektor.theorem.ca/graphics/ycbcr/ */
 enum v4l2_colorspace {
 	/*