Re: [PATCH v2 09/30] media: entity: Swap pads if route is checked from source to sink

[Jacopo Mondi <jacopo@jmondi.org>]

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HI Laurent,

On Tue, Mar 05, 2019 at 10:04:58PM +0200, Laurent Pinchart wrote:
> Hi Jacopo,
>
> On Mon, Mar 04, 2019 at 01:35:36PM +0100, Jacopo Mondi wrote:
> > On Fri, Feb 22, 2019 at 02:18:11PM +0200, Laurent Pinchart wrote:
> > > On Mon, Feb 18, 2019 at 10:21:07AM +0100, Jacopo Mondi wrote:
> > >> On Tue, Jan 22, 2019 at 05:20:30PM +0200, Laurent Pinchart wrote:
> > >>> On Tue, Jan 22, 2019 at 05:15:06PM +0200, Sakari Ailus wrote:
> > >>>> On Wed, Jan 16, 2019 at 12:57:43AM +0200, Laurent Pinchart wrote:
> > >>>>>>
> > >>>>>> This way the pads are always passed to the has_route() op sink pad first.
> > >>>>>> Makes sense.
> > >>>>>
> > >>>>> Is there anything in the API that mandates one pad to be a sink and the
> > >>>>> other pad to the a source ? I had designed the operation to allow
> > >>>>> sink-sink and source-source connections to be checked too.
> > >>>>
> > >>>> Do you have a use case in mind for sink--sink or source--source routes? The
> > >>>> routes are about flows of data, so I'd presume only source--sink or
> > >>>> sink--source routes are meaningful.
> > >>>>
> > >>>> If you did, then the driver would have to handle that by itself. This still
> > >>>> simplifies the implementation for drivers that do not.
> > >>>
> > >>> I don't have use cases for such routes, but we use the has_route
> > >>> operation when traversing pipelines, and at that point we need to get
> > >>> all the internally connected pads. In another patch in this series you
> > >>> implement a helper function that handles this, but its implementation
> > >>> isn't complete. I explained in my review of that patch that I fear a
> > >>> correct generic implementation would become quite complex, while the
> > >>> complexity should be easy to handle on the driver side as the code can
> > >>> then be specialized for the case at hand.
> > >>>
> > >>
> > >> As a compromise, in v3 I'm thinking of maintaining support for the
> > >> most common case of two sources connected to the same sink, as
> > >> Sakari's patch does, but let more complex cases be handled by the
> > >> driver implementation of has_route().
> > >>
> > >> Ack?
> > >
> > > I fear this will be confusing for subdevs, as they would have to
> > > implement part of the operation.
> > >
> > > Could it be that the subdev has_route operation isn't the best API for
> > > the job, if it gets that complex ? I wonder if it would be easier to
> > > create another operation that takes a pad index as argument, and returns
> > > the list of pads (possibly as a bitmask ?) or connected pads.
> > > media_entity_has_route() could easily be implemented on top of that, and
> > > these new semantics may be easier for subdevs to implement.
> > >
> >
> > I see, but if subdevs can easily elaborate that list, they could as
> > well easily check if the pad provided as argument is on that list.
>
> Possibly. In any case, if we keep this operation as-is, I wouldn't try
> to split the logic between the subdev drivers and the core, that would
> be asking for trouble. If it gets too complex to implement for subdev
> drivers, then we need a different operation with a different logic in
> the subdev API, and a helper that wraps around it.

In v3 I have removed support for indirect routes from the framework
part. It's all on the subdevice driver for now.
>
> > >>>>> If your goal is to simplify the implementation of the .has_route()
> > >>>>> operation in drivers, I would instead sort pad0 and pad1 by value.
> > >>>>
> > >>>> That'd be another option to make the order deterministic for the driver.
> > >>>> I'm fine with that as well.
> > >>
> > >> In v3 I have taken both suggestions in: try the "sink then source" order
> > >> first, then order by index in case the pads are of the same time. This
> > >> needs to be documented in has_route() operation definition though.
> > >>
> > >> Would that be fine with you?
> > >
> > > I think that's the worst of both worlds from a subdev point of view :-)
> >
> > Possibly :)
> >
> > Should we drop completely the sink-source ordering in favour of
> > ordering by value, and drop [15/30] that adds support for trivial
> > indirect routes?
> >
> > Let's reach consensus so I could send v3.
>
> I would certainly drop 15/30, and I don't think ordering by value would
> help subdev drivers much.

Yes, but sorting by index makes it easier to deal with the sink-sink
and source-source use cases, if the subdevice supports indirect
routes.

I have dropped 15/30 and specified pads are passed by index in v3.

Thanks
  j

>
> > >>>>>> Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
> > >>>>>> Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
> > >>>>>> ---
> > >>>>>>  drivers/media/media-entity.c | 4 ++++
> > >>>>>>  1 file changed, 4 insertions(+)
> > >>>>>>
> > >>>>>> diff --git a/drivers/media/media-entity.c b/drivers/media/media-entity.c
> > >>>>>> index 3c0e7425c8983b45..33f00e35ccd92c6f 100644
> > >>>>>> --- a/drivers/media/media-entity.c
> > >>>>>> +++ b/drivers/media/media-entity.c
> > >>>>>> @@ -249,6 +249,10 @@ bool media_entity_has_route(struct media_entity *entity, unsigned int pad0,
> > >>>>>>  	if (!entity->ops || !entity->ops->has_route)
> > >>>>>>  		return true;
> > >>>>>>
> > >>>>>> +	if (entity->pads[pad0].flags & MEDIA_PAD_FL_SOURCE
> > >>>>>> +	    && entity->pads[pad1].flags & MEDIA_PAD_FL_SINK)
> > >>>>>> +		swap(pad0, pad1);
> > >>>>>> +
> > >>>>>>  	return entity->ops->has_route(entity, pad0, pad1);
> > >>>>>>  }
> > >>>>>>  EXPORT_SYMBOL_GPL(media_entity_has_route);
>
> --
> Regards,
>
> Laurent Pinchart

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