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

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Date:   Wed, 20 Dec 2017 18:24:17 +0900
From:   Alexandre Courbot <acourbot@...omium.org>
To:     Nicolas Dufresne <nicolas@...fresne.ca>
Cc:     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>,
        Linux Media Mailing List <linux-media@...r.kernel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 0/9] media: base request API support

On Sat, Dec 16, 2017 at 6:02 AM, Nicolas Dufresne <nicolas@...fresne.ca> wrote:
> 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
>>
>> 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
>
> It looks like the example uses Hans control work you just mention.
> Notably, it uses v4l2_ext_controls ctrls.request.

Oops, I indeed forgot to remove that bit. You will want to edit that
line out if trying to compile.