Re: [PATCH v9 33/36] media: subdev: add "opposite" stream helper funcs

[Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>]

On 10/10/2021 17:15, Laurent Pinchart wrote:
> Hi Tomi,
> 
> Thank you for the patch.
> 
> On Tue, Oct 05, 2021 at 11:57:47AM +0300, Tomi Valkeinen wrote:
>> Add two helper functions to make dealing with streams easier:
>>
>> v4l2_state_find_opposite_end - given a routing table and a pad + stream,
>> return the pad + stream on the opposite side of the subdev.
>>
>> v4l2_state_get_opposite_stream_format - return a pointer to the format
>> on the pad + stream on the opposite side from the given pad + stream.
>>
>> Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
>> ---
>>   drivers/media/v4l2-core/v4l2-subdev.c | 42 +++++++++++++++++++++++++++
>>   include/media/v4l2-subdev.h           | 32 ++++++++++++++++++++
>>   2 files changed, 74 insertions(+)
>>
>> diff --git a/drivers/media/v4l2-core/v4l2-subdev.c b/drivers/media/v4l2-core/v4l2-subdev.c
>> index 37e2e1f907fc..9eeadad997c8 100644
>> --- a/drivers/media/v4l2-core/v4l2-subdev.c
>> +++ b/drivers/media/v4l2-core/v4l2-subdev.c
>> @@ -1484,3 +1484,45 @@ v4l2_state_get_stream_format(struct v4l2_subdev_state *state, unsigned int pad,
>>   	return NULL;
>>   }
>>   EXPORT_SYMBOL_GPL(v4l2_state_get_stream_format);
>> +
>> +int v4l2_state_find_opposite_end(struct v4l2_subdev_krouting *routing, u32 pad,
>> +				 u32 stream, u32 *other_pad, u32 *other_stream)
> 
> This function should take a state pointer given its name. I would also
> rename it to v4l2_subdev_state_find_opposite_end(). Same for
> v4l2_state_get_opposite_stream_format() which should be
> v4l2_subdev_state_get_opposite_stream_format().

It doesn't need the state. I think it's better to rename this to 
v4l2_routing_find_opposite_end(). Or 
v4l2_subdev_routing_find_opposite_end() if you want the "subdev" to be 
there.

>> +{
>> +	unsigned int i;
>> +
>> +	for (i = 0; i < routing->num_routes; ++i) {
>> +		struct v4l2_subdev_route *route = &routing->routes[i];
>> +
>> +		if (route->source_pad == pad &&
>> +		    route->source_stream == stream) {
>> +			*other_pad = route->sink_pad;
>> +			*other_stream = route->sink_stream;
> 
> Can we support other_stream being NULL ? When the subdev implements the
> routing API without multiplexed streams, the other_stream number will
> always be 0 and it would be nice if the caller didn't have to declare a
> placeholder variable.
> 
> There are less use cases for other_pad being NULL, but maybe we could
> also allow that for consistency reasons ? Up to you.

Sure. But are you sure the ignored stream is 0? Should the function 
verify that the stream is indeed 0 if other_stream is NULL?

For the pad, I don't know when it would be used, so it's perhaps better 
not to add that (as we can't have similar validation as for the stream).

  Tomi