Hi, On 5/29/20 10:27 AM, Tomasz Figa wrote: > [Fixing Niklas's address.] > > On Fri, May 29, 2020 at 3:26 PM Tomasz Figa <tfiga@xxxxxxxxxxxx> wrote: >> >> On Thu, May 28, 2020 at 6:21 PM Dafna Hirschfeld >> <dafna.hirschfeld@xxxxxxxxxxxxx> wrote: >>> >>> 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@xxxxxxxxxxxxx> 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? >>> >> >> I'm not very familiar with the older camera I/F drivers, but multiple >> streams isn't anything unusual for camera hardware. I recall the old >> Samsung FIMC already having support for separate preview and capture >> outputs. >> >> Also adding the reference counting on framework level probably >> wouldn't really hurt drivers which only have 1 stream anyway. >> >>>>> 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. >> >> Sorry, just thinking out loud. Generally if we look at other kAPIs, >> such as the drm_crtc_helper_funcs [1] or regulator_ops [2], the driver >> provided implementation doesn't have to care about duplicate >> enable/disable requests. Thanks for this pointer. >> >> [1] https://elixir.bootlin.com/linux/v5.7-rc7/source/include/drm/drm_modeset_helper_vtables.h#L61 >> [2] https://elixir.bootlin.com/linux/v5.7-rc7/source/include/linux/regulator/driver.h#L144 >> >> If we could prohibit calling v4l2_subdev_ops::s_stream() by the >> drivers directly and instead add something like >> v4l2_subdev_s_stream(), the latter could do reference counting on its >> own and then only call v4l2_subdev_ops::s_stream() when the reference >> count changes between 0 and 1. This is basically how v3 was implemented https://patchwork.kernel.org/patch/11489583/ And the main concern (from what I understood) was to add a stream_count under struct v4l2_subdev, that is only touched by the helpers, so this stream_count field would be useless for drivers not using the helpers. which, imho, it is not a big problem. I think we gain more with a common implementation. >> >> One problem I see with this series is that I'm not sure if it's always >> guaranteed that all the drivers in the pipeline would actually use the >> generic helpers. I'm not sure we should always guarantee usage of generic helpers, since drivers may want to initialize subdevices in a specific order. >> If there is a driver in the pipeline which just calls >> v4l2_subdev_ops::s_stream() on some other subdev on its own, it >> wouldn't be aware of the reference count and bad things could happen >> (e.g. the subdev stopped despite the count being > 0). I don't think this is a problem, since v4l2_subdev_ops::s_stream() are usually triggered by a STREAM_ON on a video node. So or the video node driver uses the helpers, or it calls v4l2_subdev_ops::s_stream() on subdevices directly. Unless if, we could have a case where we have multiple video nodes in the same topology that is implemented by different drivers, which seems odd to me. Regards, Helen >> >> However, I'm afraid this is more of the kAPI design issue and could be >> require quite a significant effort to be straightened out. >> >> Best regards, >> Tomasz >> >>> >>> 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). >>>>
