Re: [PATCH v4 0/5] media: add v4l2_pipeline_stream_{enable,disable}

[Dafna Hirschfeld <dafna.hirschfeld@collabora.com>]

Hi Tomasz, Helen, Laurent

On 26.05.20 20:57, Laurent Pinchart wrote:
> Hi Tomasz,
> 
> On Tue, May 26, 2020 at 06:11:00PM +0200, Tomasz Figa wrote:
>> On Fri, May 22, 2020 at 11:06 AM Helen Koike <helen.koike@collabora.com> wrote:
>>> On 5/22/20 4:55 AM, Dafna Hirschfeld wrote:
>>>> Hi,
>>>> This is v4 of the patchset that was sent by Helen Koike.
>>>>
>>>> Media drivers need to iterate through the pipeline and call .s_stream()
>>>> callbacks in the subdevices.
>>>>
>>>> Instead of repeating code, add helpers for this.
>>>>
>>>> These helpers will go walk through the pipeline only visiting entities
>>>> that participates in the stream, i.e. it follows links from sink to source
>>>> (and not the opposite).
>>>> For example, in a topology like this https://bit.ly/3b2MxjI
>>>> calling v4l2_pipeline_stream_enable() from rkisp1_mainpath won't call
>>>> .s_stream(true) for rkisp1_resizer_selfpath.
>>>>
>>>> stream_count variable was added in v4l2_subdevice to handle nested calls
>>>> to the helpers.
>>>> This is useful when the driver allows streaming from more then one
>>>> capture device sharing subdevices.
>>>
>>> If I understand correctly, this isn't  true anymore right? Nested calls aren't
>>> possible anymore since this version doesn't contain stream_count in struct v4l2_subdevice.
>>>
>>> Documentation of v4l2_pipeline_stream_*() should also be updated.
>>>
>>> Just to be clear, without the nested call, vimc will require to add its own
>>> counters, patch https://patchwork.kernel.org/patch/10948833/ will be
>>> required again to allow multi streaming.
>>>
>>> Also, patch "media: staging: rkisp1: cap: use v4l2_pipeline_stream_{enable,disable}"
>>> is cleaner in the previous version (with stream_count in struct v4l2_subdevice).
>>>
>>> All drivers that allows multi streaming will need to implement some special handling.
>>>
>>> Adding stream_count in struct v4l2_subdevice still seems cleaner to me. I'd like to hear
>>> what others think.
>>
>> I certainly would see this reference counting done in generic code,
>> because requiring every driver to do it simply adds to the endless

It is required only for drivers that support multistreaming. I don't know much
about other driver except of the ones I am working on, is it a common case?

>> amount of boiler plate that V4L2 currently requires from the drivers.
>> :(
>>
>> I wonder if it wouldn't be possible to redesign the framework so that
>> .s_stream() at the subdev level is only called when it's expected to
>> either start or stop this particular subdev and driver's
>> implementation can simply execute the requested action.

You mean that a generic code similar to the helper functions in this patchset
will be used for all drivers, so that drivers don't call s_stream for subdevices
anymore?
Anyway, this patchset just adds helper functions, it does not redesign the code.
Maybe the stream_count can be updated in the v4l2_subdev_call macro ?
This why it can be used not just for the helper functions.

Thanks,
Dafna

> 
> I'd very much like that. Note that I think a few drivers abuse the on
> parameter to the function to pass other values than 0 or 1. We'd have to
> fix those first (or maybe it has been done already, it's been a long
> time since I last checked).
>