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. [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. 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. 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). 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). > >
