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SubjectRe: [PATCHv3 00/11] Implement V4L2_BUF_FLAG_NO_CACHE_* flags
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On 2/26/20 12:15 PM, Sergey Senozhatsky wrote:
> Hello,
>
> V3 of the patchset, reshuffled and updated.
>
> - Most notable changes:
>
> a) Added a simple helper function vb2_queue_allows_cache_hints(),
> which return true if queue has ->allow_cache_hints and when
> ->memory is VB2_MEMORY_MMAP.
> That is - user space cache and memory consistency hints are now
> specifically for MMAP buffers and queues that support hints.
>
> b) Set V4L2_BUF_CAP_SUPPORTS_CACHE_HINTS capability bit only when queue
> has ->allow_cache_hints and ->io_modes has VB2_MMAP bit set
>
> c) Clear "incompatible" request's flags when queue does not permit
> cache and memory consistency hints (IOW, when vb2_queue_allows_cache_hints()
> return false)
>
>
> Minor changes:
>
> - Squashed V4L2_BUF_CAP_SUPPORTS_CACHE_HINTS and V4L2_FLAG_MEMORY_NON_CONSISTENT
> patches.
>
> - Added more documentation and code comments.
>
>
> Previous series:
> v2 link: https://lore.kernel.org/lkml/20200204025641.218376-1-senozhatsky@chromium.org/
> v1 link: https://lore.kernel.org/lkml/20191217032034.54897-1-senozhatsky@chromium.org/
>
>
> Series Intro
> ========================================================================
>
> This is a reworked version of the vb2 cache hints
> (V4L2_BUF_FLAG_NO_CACHE_INVALIDATE / V4L2_BUF_FLAG_NO_CACHE_CLEAN)
> support patch series which previsouly was developed by Sakari and
> Laurent [0].
>
> The patch set attempts to preserve the existing behvaiour - cache
> sync is performed in ->prepare() and ->finish() (unless the buffer
> is DMA exported). User space can request “default behavior” override
> with cache management hints, which are handled on a per-buffer basis
> and should be supplied with v4l2_buffer ->flags during buffer
> preparation. There are two possible hints:
>
> - V4L2_BUF_FLAG_NO_CACHE_INVALIDATE
> No cache sync on ->finish()
>
> - V4L2_BUF_FLAG_NO_CACHE_CLEAN
> No cache sync on ->prepare()
>
> In order to keep things on the safe side, we also require driver
> to explicitly state which of its queues (if any) support user space
> cache management hints (such queues should have ->allow_cache_hints
> bit set).
>
> The patch set also (to some extent) simplifies allocators' ->prepare()
> and ->finish() callbacks. Namely, we move cache management decision
> making to the upper - core - layer. For example, if, previously, we
> would have something like this
>
> vb2_buffer_done()
> vb2_dc_finish()
> if (buf->db_attach)
> return;
>
> where each allocators' ->finish() callback would either bail
> out (DMA exported buffer, for instance) or sync, now that "bail
> out or sync" decision is made before we call into the allocator.
>
> Along with cache management hints, user space is also able to
> adjust queue's memory consistency attributes. Memory consistency
> attribute (dma_attrs) is per-queue, yet it plays its role on the
> allocator level, when we allocate buffers’ private memory (planes).
> For the time being, only one consistency attribute is supported:
> DMA_ATTR_NON_CONSISTENT.

v3 looks very good, I only found some minor issues.

I think v4 should be ready to be merged, unless others have more comments.

Regards,

Hans

>
> [0] https://www.mail-archive.com/linux-media@vger.kernel.org/msg112459.html
>
> Sergey Senozhatsky (11):
> videobuf2: add cache management members
> videobuf2: handle V4L2 buffer cache flags
> videobuf2: add V4L2_FLAG_MEMORY_NON_CONSISTENT flag
> videobuf2: add queue memory consistency parameter
> videobuf2: handle V4L2_FLAG_MEMORY_NON_CONSISTENT flag
> videobuf2: factor out planes prepare/finish functions
> videobuf2: do not sync caches when we are allowed not to
> videobuf2: check ->synced flag in prepare() and finish()
> videobuf2: add begin/end cpu_access callbacks to dma-contig
> videobuf2: add begin/end cpu_access callbacks to dma-sg
> videobuf2: don't test db_attach in dma-contig prepare and finish
>
> Documentation/media/uapi/v4l/buffer.rst | 29 +++++
> .../media/uapi/v4l/vidioc-create-bufs.rst | 8 +-
> .../media/uapi/v4l/vidioc-reqbufs.rst | 22 +++-
> .../media/common/videobuf2/videobuf2-core.c | 110 +++++++++++++-----
> .../common/videobuf2/videobuf2-dma-contig.c | 39 ++++++-
> .../media/common/videobuf2/videobuf2-dma-sg.c | 36 ++++--
> .../media/common/videobuf2/videobuf2-v4l2.c | 82 ++++++++++++-
> drivers/media/dvb-core/dvb_vb2.c | 2 +-
> drivers/media/v4l2-core/v4l2-ioctl.c | 5 +-
> include/media/videobuf2-core.h | 28 ++++-
> include/uapi/linux/videodev2.h | 11 +-
> 11 files changed, 314 insertions(+), 58 deletions(-)
>

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