| Message ID | 20210302004624.31294-6-senozhatsky@chromium.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | videobuf2: support new noncontiguous DMA API | expand |
On 02/03/2021 01:46, Sergey Senozhatsky wrote: > By setting or clearing V4L2_FLAG_MEMORY_NON_COHERENT flag > user-space should be able to hint vb2 that either a non-coherent > (if supported) or coherent memory should be used for the buffer > allocation. > > The patch set also adds a corresponding capability flag: > fill_buf_caps() reports V4L2_BUF_CAP_SUPPORTS_MMAP_CACHE_HINTS > when queue supports user-space cache management hints. Hmm, this paragraph is probably outdated (copy and paste?) since this capability already exists. > > Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org> > --- > .../userspace-api/media/v4l/buffer.rst | 40 ++++++++++++++++++- > .../media/v4l/vidioc-reqbufs.rst | 5 ++- > include/uapi/linux/videodev2.h | 2 + > 3 files changed, 43 insertions(+), 4 deletions(-) > > diff --git a/Documentation/userspace-api/media/v4l/buffer.rst b/Documentation/userspace-api/media/v4l/buffer.rst > index 1b0fdc160533..a39852d6174f 100644 > --- a/Documentation/userspace-api/media/v4l/buffer.rst > +++ b/Documentation/userspace-api/media/v4l/buffer.rst > @@ -676,8 +676,6 @@ Buffer Flags > > \normalsize > > -.. _memory-flags: > - > enum v4l2_memory > ================ > > @@ -701,6 +699,44 @@ enum v4l2_memory > - 4 > - The buffer is used for :ref:`DMA shared buffer <dmabuf>` I/O. > > +.. _memory-flags: > + > +Memory Consistency Flags > +------------------------ > + > +.. raw:: latex > + > + \small > + > +.. tabularcolumns:: |p{7.0cm}|p{2.1cm}|p{8.4cm}| > + > +.. cssclass:: longtable > + > +.. flat-table:: > + :header-rows: 0 > + :stub-columns: 0 > + :widths: 3 1 4 > + > + * .. _`V4L2-FLAG-MEMORY-NON-COHERENT`: > + > + - ``V4L2_FLAG_MEMORY_NON_COHERENT`` Rename this to V4L2_MEMORY_FLAG_NON_COHERENT: this is consistent with V4L2_FMT_FLAG_ and V4L2_BUF_FLAG_. > + - 0x00000001 > + - A buffer is allocated either in coherent (it will be automatically > + coherent between the CPU and the bus) or non-coherent memory. The > + latter can provide performance gains, for instance the CPU cache > + sync/flush operations can be avoided if the buffer is accessed by the > + corresponding device only and the CPU does not read/write to/from that > + buffer. However, this requires extra care from the driver -- it must > + guarantee memory consistency by issuing a cache flush/sync when > + consistency is needed. If this flag is set V4L2 will attempt to > + allocate the buffer in non-coherent memory. The flag takes effect > + only if the buffer is used for :ref:`memory mapping <mmap>` I/O and the > + queue reports the :ref:`V4L2_BUF_CAP_SUPPORTS_MMAP_CACHE_HINTS > + <V4L2-BUF-CAP-SUPPORTS-MMAP-CACHE-HINTS>` capability. > + > +.. raw:: latex > + > + \normalsize > > Timecodes > ========= > diff --git a/Documentation/userspace-api/media/v4l/vidioc-reqbufs.rst b/Documentation/userspace-api/media/v4l/vidioc-reqbufs.rst > index c1c88e00b106..950e7ec1aac5 100644 > --- a/Documentation/userspace-api/media/v4l/vidioc-reqbufs.rst > +++ b/Documentation/userspace-api/media/v4l/vidioc-reqbufs.rst > @@ -154,8 +154,9 @@ aborting or finishing any DMA in progress, an implicit > - This capability is set by the driver to indicate that the queue supports > cache and memory management hints. However, it's only valid when the > queue is used for :ref:`memory mapping <mmap>` streaming I/O. See > - :ref:`V4L2_BUF_FLAG_NO_CACHE_INVALIDATE <V4L2-BUF-FLAG-NO-CACHE-INVALIDATE>` and > - :ref:`V4L2_BUF_FLAG_NO_CACHE_CLEAN <V4L2-BUF-FLAG-NO-CACHE-CLEAN>`. > + :ref:`V4L2_BUF_FLAG_NO_CACHE_INVALIDATE <V4L2-BUF-FLAG-NO-CACHE-INVALIDATE>`, > + :ref:`V4L2_BUF_FLAG_NO_CACHE_CLEAN <V4L2-BUF-FLAG-NO-CACHE-CLEAN>` and > + :ref:`V4L2_FLAG_MEMORY_NON_COHERENT <V4L2-FLAG-MEMORY-NON-COHERENT>`. > > Return Value > ============ > diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h > index 79dbde3bcf8d..b1d4171fe50b 100644 > --- a/include/uapi/linux/videodev2.h > +++ b/include/uapi/linux/videodev2.h > @@ -954,6 +954,8 @@ struct v4l2_requestbuffers { > __u32 reserved[1]; > }; > > +#define V4L2_FLAG_MEMORY_NON_COHERENT (1 << 0) > + > /* capabilities for struct v4l2_requestbuffers and v4l2_create_buffers */ > #define V4L2_BUF_CAP_SUPPORTS_MMAP (1 << 0) > #define V4L2_BUF_CAP_SUPPORTS_USERPTR (1 << 1) > Regards, Hans
diff --git a/Documentation/userspace-api/media/v4l/buffer.rst b/Documentation/userspace-api/media/v4l/buffer.rst index 1b0fdc160533..a39852d6174f 100644 --- a/Documentation/userspace-api/media/v4l/buffer.rst +++ b/Documentation/userspace-api/media/v4l/buffer.rst @@ -676,8 +676,6 @@ Buffer Flags \normalsize -.. _memory-flags: - enum v4l2_memory ================ @@ -701,6 +699,44 @@ enum v4l2_memory - 4 - The buffer is used for :ref:`DMA shared buffer <dmabuf>` I/O. +.. _memory-flags: + +Memory Consistency Flags +------------------------ + +.. raw:: latex + + \small + +.. tabularcolumns:: |p{7.0cm}|p{2.1cm}|p{8.4cm}| + +.. cssclass:: longtable + +.. flat-table:: + :header-rows: 0 + :stub-columns: 0 + :widths: 3 1 4 + + * .. _`V4L2-FLAG-MEMORY-NON-COHERENT`: + + - ``V4L2_FLAG_MEMORY_NON_COHERENT`` + - 0x00000001 + - A buffer is allocated either in coherent (it will be automatically + coherent between the CPU and the bus) or non-coherent memory. The + latter can provide performance gains, for instance the CPU cache + sync/flush operations can be avoided if the buffer is accessed by the + corresponding device only and the CPU does not read/write to/from that + buffer. However, this requires extra care from the driver -- it must + guarantee memory consistency by issuing a cache flush/sync when + consistency is needed. If this flag is set V4L2 will attempt to + allocate the buffer in non-coherent memory. The flag takes effect + only if the buffer is used for :ref:`memory mapping <mmap>` I/O and the + queue reports the :ref:`V4L2_BUF_CAP_SUPPORTS_MMAP_CACHE_HINTS + <V4L2-BUF-CAP-SUPPORTS-MMAP-CACHE-HINTS>` capability. + +.. raw:: latex + + \normalsize Timecodes ========= diff --git a/Documentation/userspace-api/media/v4l/vidioc-reqbufs.rst b/Documentation/userspace-api/media/v4l/vidioc-reqbufs.rst index c1c88e00b106..950e7ec1aac5 100644 --- a/Documentation/userspace-api/media/v4l/vidioc-reqbufs.rst +++ b/Documentation/userspace-api/media/v4l/vidioc-reqbufs.rst @@ -154,8 +154,9 @@ aborting or finishing any DMA in progress, an implicit - This capability is set by the driver to indicate that the queue supports cache and memory management hints. However, it's only valid when the queue is used for :ref:`memory mapping <mmap>` streaming I/O. See - :ref:`V4L2_BUF_FLAG_NO_CACHE_INVALIDATE <V4L2-BUF-FLAG-NO-CACHE-INVALIDATE>` and - :ref:`V4L2_BUF_FLAG_NO_CACHE_CLEAN <V4L2-BUF-FLAG-NO-CACHE-CLEAN>`. + :ref:`V4L2_BUF_FLAG_NO_CACHE_INVALIDATE <V4L2-BUF-FLAG-NO-CACHE-INVALIDATE>`, + :ref:`V4L2_BUF_FLAG_NO_CACHE_CLEAN <V4L2-BUF-FLAG-NO-CACHE-CLEAN>` and + :ref:`V4L2_FLAG_MEMORY_NON_COHERENT <V4L2-FLAG-MEMORY-NON-COHERENT>`. Return Value ============ diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h index 79dbde3bcf8d..b1d4171fe50b 100644 --- a/include/uapi/linux/videodev2.h +++ b/include/uapi/linux/videodev2.h @@ -954,6 +954,8 @@ struct v4l2_requestbuffers { __u32 reserved[1]; }; +#define V4L2_FLAG_MEMORY_NON_COHERENT (1 << 0) + /* capabilities for struct v4l2_requestbuffers and v4l2_create_buffers */ #define V4L2_BUF_CAP_SUPPORTS_MMAP (1 << 0) #define V4L2_BUF_CAP_SUPPORTS_USERPTR (1 << 1)
By setting or clearing V4L2_FLAG_MEMORY_NON_COHERENT flag user-space should be able to hint vb2 that either a non-coherent (if supported) or coherent memory should be used for the buffer allocation. The patch set also adds a corresponding capability flag: fill_buf_caps() reports V4L2_BUF_CAP_SUPPORTS_MMAP_CACHE_HINTS when queue supports user-space cache management hints. Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org> --- .../userspace-api/media/v4l/buffer.rst | 40 ++++++++++++++++++- .../media/v4l/vidioc-reqbufs.rst | 5 ++- include/uapi/linux/videodev2.h | 2 + 3 files changed, 43 insertions(+), 4 deletions(-)