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

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Date:   Fri, 12 Jan 2018 12:45:56 +0100
From:   Hans Verkuil <hverkuil@...all.nl>
To:     Alexandre Courbot <acourbot@...omium.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        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

Hi Alexandre,

On 12/15/17 08:56, Alexandre Courbot wrote:
> 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
> 
> 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!

I think this will become more interesting when the control code is in.

The main thing I've noticed with this patch series is that it is very codec
oriented. Which in some ways is OK (after all, that's the first type of HW
that we want to support), but the vb2 code in particular should be more
generic.

I would also recommend that you start preparing documentation patches: we
can review that and make sure all the corner-cases are correctly documented.

The public API changes are (I think) fairly limited, but the devil is in
the details, so getting that reviewed early on will help you later.

It's a bit unfortunate that the fence patch series is also making vb2 changes,
but I hope that will be merged fairly soon so you can develop on top of that
series.

Regards,

	Hans

> 
> 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
>