[Intel-gfx] [PATCH v2 1/4] drm/i915: Add audio set_ncts callback

[Yang, Libin]

Hi Jani,

Thanks for reviewing, please see my comments

> -----Original Message-----
> From: Jani Nikula [mailto:jani.nikula at linux.intel.com]
> Sent: Monday, August 10, 2015 7:46 PM
> To: Yang, Libin; alsa-devel at alsa-project.org; tiwai at suse.de; intel-
> gfx at lists.freedesktop.org; daniel.vetter at ffwll.ch
> Subject: Re: [Intel-gfx] [PATCH v2 1/4] drm/i915: Add audio set_ncts
> callback
> 
> On Mon, 10 Aug 2015, libin.yang at intel.com wrote:
> > From: Libin Yang <libin.yang at intel.com>
> >
> > Add the set_ncts callback.
> >
> > With the callback, audio driver can trigger
> > i915 driver to set the proper N/CTS
> > based on different sample rates.
> >
> > Signed-off-by: Libin Yang <libin.yang at intel.com>
> > ---
> >  include/drm/i915_component.h | 2 ++
> >  1 file changed, 2 insertions(+)
> >
> > diff --git a/include/drm/i915_component.h
> b/include/drm/i915_component.h
> > index c9a8b64..7305881 100644
> > --- a/include/drm/i915_component.h
> > +++ b/include/drm/i915_component.h
> > @@ -33,6 +33,8 @@ struct i915_audio_component {
> >  		void (*put_power)(struct device *);
> >  		void (*codec_wake_override)(struct device *, bool
> enable);
> >  		int (*get_cdclk_freq)(struct device *);
> > +		int (*set_ncts)(struct device *, int port, int dev_entry,
> > +					int rate);
> 
> I'd rather call this set_audio_rate or similar, and dropping the
> references to N and CTS. The caller does not need to know.

But it seems the set_audio_rate will confuse the user. From the
literal meaning, it is setting the rate of audio, such as sample rate,
which will make audio driver developers confused.
And the function is just setting N/CTS which is defined from 
HDMI SPEC.

BTW: your comment reminds me that get_cdclk_freq() seems
to need change the name as cdclk is not in the open spec.

> 
> I'm also not fond of adding a dev_entry parameter and leaving it
> unused. I do not think we know specifically how we're going to identify
> MST sinks, and the interface may need to be changed anyway. Let's
> force
> an update in the caller side as well when there's actually sensible
> support in our side.

The device entry is a concept in HDA spec. For driver implementation,
I think we can use an int variable or a struct device to represent it.
A int variable is an easy way. There is some place in audio driver using
int variable to represent the deivce entry. And audio driver will not
care how gfx driver supports the DP1.2 MST, I mean audio driver will
not know the structures inside gfx driver.

I will remove this parameter in this version if you are thinking the
MST interface is indeterminate. 

BTW: do you know when gfx will normally support MST?

Best Regards,
Libin

> 
> BR,
> Jani.
> 
> >  	} *ops;
> >  };
> >
> > --
> > 1.9.1
> >
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> > Intel-gfx at lists.freedesktop.org
> > http://lists.freedesktop.org/mailman/listinfo/intel-gfx
> 
> --
> Jani Nikula, Intel Open Source Technology Center