Re: [RFC PATCH v1 3/5] media: tegra-video: Move PM runtime handle to streaming

[Sowjanya Komatineni]

On 4/28/20 8:15 AM, Dmitry Osipenko wrote:
> External email: Use caution opening links or attachments
>
>
> 28.04.2020 18:08, Sowjanya Komatineni ÐÐÑÐÑ:
> > On 4/28/20 7:59 AM, Dmitry Osipenko wrote:
> > > External email: Use caution opening links or attachments
> > >
> > >
> > > 28.04.2020 17:51, Sowjanya Komatineni ÐÐÑÐÑ:
> > > > On 4/28/20 6:59 AM, Dmitry Osipenko wrote:
> > > > > External email: Use caution opening links or attachments
> > > > >
> > > > >
> > > > > 28.04.2020 07:20, Sowjanya Komatineni ÐÐÑÐÑ:
> > > > > > diff --git a/drivers/staging/media/tegra-video/csi.c
> > > > > > b/drivers/staging/media/tegra-video/csi.c
> > > > > > index b3dd0c3..29ccdae 100644
> > > > > > --- a/drivers/staging/media/tegra-video/csi.c
> > > > > > +++ b/drivers/staging/media/tegra-video/csi.c
> > > > > > @@ -272,8 +272,25 @@ static int tegra_csi_s_stream(struct v4l2_subdev
> > > > > > *subdev, int enable)
> > > > > >          struct tegra_vi_channel *chan =
> > > > > > v4l2_get_subdev_hostdata(subdev);
> > > > > >          struct tegra_csi_channel *csi_chan = to_csi_chan(subdev);
> > > > > >          struct tegra_csi *csi = csi_chan->csi;
> > > > > > +     int ret;
> > > > > > +
> > > > > > +     if (enable && atomic_add_return(1, &csi->clk_refcnt) == 1) {
> > > > > > +             ret = pm_runtime_get_sync(csi->dev);
> > > > > > +             if (ret < 0) {
> > > > > > +                     dev_err(csi->dev,
> > > > > > +                             "failed to get runtime PM: %d\n", ret);
> > > > > > +                     pm_runtime_put_noidle(csi->dev);
> Why this pm_runtime_put_noidle() is needed? This should be wrong, please
> remove it.

pm_runtime_get_sync() increments power.usage_count prior to rpm_resume

if rpm_resume fails it does not decrement usage_count.

So to balance count on failure, calling pm_runtime_put_noidle()

> > > > > > +                     atomic_dec(&csi->clk_refcnt);
> > > > > > +                     return ret;
> > > > > > +             }
> > > > > > +     }
> > > > > > +
> > > > > > +     ret = csi->ops->csi_streaming(csi_chan, chan->pg_mode, enable);
> > > > > >
> > > > > > -     return csi->ops->csi_streaming(csi_chan, chan->pg_mode, enable);
> > > > > > +     if ((ret < 0 || !enable) &&
> > > > > > atomic_dec_and_test(&csi->clk_refcnt))
> > > > > > +             pm_runtime_put_sync(csi->dev);
> > > > > Runtime PM maintains its own refcount, why these
> > > > > clk_refcnt/power_on_refcnt are needed?
> > > > Streaming is per channel and we can't turn power/clocks off while other
> > > > channels may still be running.
> > > All channels use the same CSI device. You should remove the custom
> > > refcounting.
> > >
> > > BTW, next time you'll really need to do refcounting, use the generic
> > > kref.
> > Before channel stream we enable power/clocks and after streaming we stop.
> >
> > So without refcount, on stream stop of any of the channel RPM put turns
> > power/clock but other channels will still be streaming.
> Runtime PM uses its own refcounting. Please consult the RPM code and
> documentation.
>
> https://elixir.bootlin.com/linux/v5.7-rc3/source/include/linux/pm_runtime.h#L78
> https://elixir.bootlin.com/linux/v5.7-rc3/source/drivers/base/power/runtime.c#L1079
Got it. Will remove refcount for RPM put/get