Re: [PATCH] media: v4l2-subdev.h: drop the guard CONFIG_VIDEO_V4L2_SUBDEV_API for v4l2_subdev_get_try_*()

From: Hans Verkuil
Date: Tue Dec 02 2014 - 02:45:58 EST

On 12/02/2014 12:26 AM, Laurent Pinchart wrote:
> Hi Prabhakar,
> On Sunday 30 November 2014 21:30:35 Prabhakar Lad wrote:
>> On Sun, Nov 30, 2014 at 9:16 PM, Laurent Pinchart wrote:
>>> On Sunday 30 November 2014 21:05:50 Prabhakar Lad wrote:
>>>> On Sat, Nov 29, 2014 at 7:12 PM, Laurent Pinchart wrote:
>>>>> Hi Prabhakar,
>>>> [Snip]
>>>>>>> Sure. That's a better choice than removing the config option
>>>>>>> dependency of the fields struct v4l2_subdev.
>>>>> Decoupling CONFIG_VIDEO_V4L2_SUBDEV_API from the availability of the
>>>>> in-kernel pad format and selection rectangles helpers is definitely a
>>>>> good idea. I was thinking about decoupling the try format and
>>>>> rectangles from v4l2_subdev_fh by creating a kind of configuration store
>>>>> structure to store them, and embedding that structure in v4l2_subdev_fh.
>>>>> The pad-level operations would then take a pointer to the configuration
>>>>> store instead of the v4l2_subdev_fh. Bridge drivers that want to
>>>>> implement TRY_FMT based on pad-level operations would create a
>>>>> configuration store, use the pad-level operations, and destroy the
>>>>> configuration store. The userspace subdev API would use the
>>>>> configuration store from the file handle.
>>>> are planning to work/post any time soon ? Or are you OK with suggestion
>>>> from Hans ?
>>> I have no plan to work on that myself now, I was hoping you could
>>> implement it ;-)
>> OK will implement it.
>> Can you please elaborate a more on this "The userspace subdev API would use
>> the configuration store from the file handle."
> Basically,
> 1. Create a subdev pad configuration store structure to store the formats and
> selection rectangles for each pad.

I wouldn't call it a 'store'. Just call it fmt_config or pad_config something like

> 2. Embed an instance of that structure in v4l2_subdev_fh.
> 3. Modify the subdev pad ops to take a configuration store pointer instead of
> a file handle pointer.
> The userspace API implementation (v4l2-subdev.c) would then pass &fh->store to
> the pad operations instead of fh.
> Bridge drivers that need to implement TRY_FMT on top of pad ops would create a
> temporary store (or temporary stores when multiple subsdevs are involved),
> call the pad ops with a pointer to the temporary store to propagate TRY
> formats, destroy the store(s) and return the resulting format.

That will work. I think this is a good approach and it shouldn't be too difficult.


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