[alsa-devel] [PATCH 1/7] video: add HDMI state notifier support

[Cheng-yi Chiang]

On Fri, Jun 21, 2019 at 5:12 AM Daniel Vetter <daniel at ffwll.ch> wrote:
>
> Massively cutting this thread, since halfway through in my previous reply
> I realized that maybe hdmi_codec is a much better starting point.
>
ACK
> On Thu, Jun 20, 2019 at 09:23:23PM +0800, Cheng-yi Chiang wrote:
> > On Thu, Jun 20, 2019 at 5:25 PM Daniel Vetter <daniel at ffwll.ch> wrote:
> > > Yeah fully agreeing that hdmi_audio_code is probably a better starting
> > > point. Problem is that becuase hdmi_codec is built on top of platform
> > > device it's quite a bit harder to extend with callbacks and things like
> > > that, without breaking the driver model.
> > >
> > > I need to think about this more, but if all we need to look at is
> > > hdmi_codec, then I think this becomes a lot easier. And we can ignore
> > > drm_audio_component.h completely.
> >
> >
> > It is surprising that you think this way.
> > Maybe the original patch before hdmi-notifier was introduced is the
> > better way to solve this issue, if we only need to look at hdmi_codec.
> >
> > The history of hdmi_codec driver is in this patch series:
> >
> > https://lore.kernel.org/patchwork/patch/539656/
>
> Hm, this doesn't seem to be the hdmi_codec driver I meant, but another,
> new one. I was talking about SND_SOC_HDMI_CODEC.
>
Yes you are right. They are different codec drivers.
Sorry for the confusion. What I meant was that my use case on RK3288
was using dw-hdmi-audio.c codec driver,
which was later replaced by a more general version hdmi-codec.c.

> > There was a callback mechanism implemented between dw-hdmi and hdmi
> > codec driver.
> > It was later consolidated by Doug in this patch for better jack status
> > reporting:
> >
> > https://chromium-review.googlesource.com/c/chromiumos/third_party/kernel/+/303573/
>
> Hm that still seems entirely separate hdmi-codec specific to dw-hdmi only
> ...
>
Again you are right. Sorry for the confusion. What I meant is that
this callback mechanism should work on hdmi-codec.c driver as well.

> > I am not sure why the original patch series did not get fully accepted
> > in the upstream.
> > It was quite long time ago.
> >
> > But if you think this might be the right way to do, then it is even
> > better for us because the patch series and Doug's patch had been quite
> > stable
> > on our RK3288 products for about four years with plenty of users, so
> > we have much higher confidence in them.
> > I can rebase and clean up them and post another patch for review.
> >
> > Please let me know what approach you feel is better.
> > Thanks again!
>
> Not sure we're talking about the same. What I had in mind is to add jack
> status to the hdmi-codec.c stuff, which is used by multiple soc drm
> display drivers already. Looking at git grep output, there seems to be
> already some support for dw-hdmi synopsys drm_bridge driver. I thought of
> extending that. Does that not work for you?
>
I think extending current interface will work.
There is a struct hdmi_codec_pdata to let ALSA codec driver access
some ops through platform data.
And after this patch

https://lore.kernel.org/patchwork/patch/692324/

ALSA codec driver can get access to the struct on DRM side.
Based on this I can add a new ops to register callback function for jack status.
It will be similar to Doug's chromium patch above.
I think that is quite a feasible way, and can benefit all boards using
hdmi-codec.c.

Thanks a lot!!

> Thanks, Daniel
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch