linux-kernel - Re: [RFC PATCH 0/9] media: base request API support

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Date:   Fri, 15 Dec 2017 16:04:44 -0500
From:   Nicolas Dufresne <nicolas@...fresne.ca>
To:     Alexandre Courbot <acourbot@...omium.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Hans Verkuil <hverkuil@...all.nl>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Pawel Osciak <posciak@...omium.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Tomasz Figa <tfiga@...omium.org>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Gustavo Padovan <gustavo.padovan@...labora.com>
Cc:     linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 0/9] media: base request API support

Le vendredi 15 décembre 2017 à 16:56 +0900, Alexandre Courbot a écrit :
> Here is a new attempt at the request API, following the UAPI we agreed on in
> Prague. Hopefully this can be used as the basis to move forward.
> 
> This series only introduces the very basics of how requests work: allocate a
> request, queue buffers to it, queue the request itself, wait for it to complete,
> reuse it. It does *not* yet use Hans' work with controls setting. I have
> preferred to submit it this way for now as it allows us to concentrate on the
> basic request/buffer flow, which was harder to get properly than I initially
> thought. I still have a gut feeling that it can be improved, with less back-and-
> forth into drivers.
> 
> Plugging in controls support should not be too hard a task (basically just apply
> the saved controls when the request starts), and I am looking at it now.
> 
> The resulting vim2m driver can be successfully used with requests, and my tests
> so far have been successful.
> 
> There are still some rougher edges:
> 
> * locking is currently quite coarse-grained
> * too many #ifdef CONFIG_MEDIA_CONTROLLER in the code, as the request API
>   depends on it - I plan to craft the headers so that it becomes unnecessary.
>   As it is, some of the code will probably not even compile if
>   CONFIG_MEDIA_CONTROLLER is not set

Would it be possible to explain why this relation between request and
the media controller ? Why couldn't request be created from video
devices ?

> 
> But all in all I think the request flow should be clear and easy to review, and
> the possibility of custom queue and entity support implementations should give
> us the flexibility we need to support more specific use-cases (I expect the
> generic implementations to be sufficient most of the time though).
> 
> A very simple test program exercising this API is available here (don't forget
> to adapt the /dev/media0 hardcoding):
> https://gist.github.com/Gnurou/dbc3776ed97ea7d4ce6041ea15eb0438
> 
> Looking forward to your feedback and comments!
> 
> Alexandre Courbot (8):
>   media: add request API core and UAPI
>   media: request: add generic queue
>   media: request: add generic entity ops
>   media: vb2: add support for requests
>   media: vb2: add support for requests in QBUF ioctl
>   media: v4l2-mem2mem: add request support
>   media: vim2m: add media device
>   media: vim2m: add request support
> 
> Hans Verkuil (1):
>   videodev2.h: Add request field to v4l2_buffer
> 
>  drivers/media/Makefile                        |   4 +-
>  drivers/media/media-device.c                  |   6 +
>  drivers/media/media-request-entity-generic.c  |  56 ++++
>  drivers/media/media-request-queue-generic.c   | 150 ++++++++++
>  drivers/media/media-request.c                 | 390 ++++++++++++++++++++++++++
>  drivers/media/platform/vim2m.c                |  46 +++
>  drivers/media/usb/cpia2/cpia2_v4l.c           |   2 +-
>  drivers/media/v4l2-core/v4l2-compat-ioctl32.c |   7 +-
>  drivers/media/v4l2-core/v4l2-ioctl.c          |  99 ++++++-
>  drivers/media/v4l2-core/v4l2-mem2mem.c        |  34 +++
>  drivers/media/v4l2-core/videobuf2-core.c      |  59 +++-
>  drivers/media/v4l2-core/videobuf2-v4l2.c      |  32 ++-
>  include/media/media-device.h                  |   3 +
>  include/media/media-entity.h                  |   6 +
>  include/media/media-request.h                 | 282 +++++++++++++++++++
>  include/media/v4l2-mem2mem.h                  |  19 ++
>  include/media/videobuf2-core.h                |  25 +-
>  include/media/videobuf2-v4l2.h                |   2 +
>  include/uapi/linux/media.h                    |  11 +
>  include/uapi/linux/videodev2.h                |   3 +-
>  20 files changed, 1216 insertions(+), 20 deletions(-)
>  create mode 100644 drivers/media/media-request-entity-generic.c
>  create mode 100644 drivers/media/media-request-queue-generic.c
>  create mode 100644 drivers/media/media-request.c
>  create mode 100644 include/media/media-request.h
> 
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