Re: [PATCH 00/11] drm/vc4: hdmi: Enable Channel Mapping, IEC958, HBR Passthrough using hdmi-codec

[Takashi Iwai]

On Tue, 25 May 2021 11:23:53 +0200,
Maxime Ripard wrote:
> 
> Hi Takashi,
> 
> On Tue, May 25, 2021 at 10:35:14AM +0200, Takashi Iwai wrote:
> > On Mon, 24 May 2021 15:39:04 +0200,
> > Maxime Ripard wrote:
> > > 
> > > Hi,
> > > 
> > > On Fri, May 07, 2021 at 04:03:23PM +0200, Maxime Ripard wrote:
> > > > Hi,
> > > > 
> > > > hdmi-codec allows to have a lot of HDMI-audio related infrastructure in place,
> > > > it's missing a few controls to be able to provide HBR passthrough. This series
> > > > adds more infrastructure for the drivers, and leverages it in the vc4 HDMI
> > > > controller driver.
> > > > 
> > > > One thing that felt a bit weird is that even though
> > > > https://www.kernel.org/doc/html/latest/sound/kernel-api/writing-an-alsa-driver.html#iec958-s-pdif
> > > > mentions that the iec958 mask control should be a mixer control and the
> > > > default control should be a PCM one, it feels a bit weird to have two different
> > > > control type for two controls so similar, and other drivers are pretty
> > > > inconsistent with this. Should we update the documentation?
> > > 
> > > Any comments on this series?
> > 
> > A patch for updating the documentation is welcome.
> > Currently, as de facto standard, we allow both MIXER and PCM ifaces
> > for all IEC958-related controls, and it's unlikely that we would
> > change that in future.
> 
> Ok, I'll write a patch for the documentation make it clearer then :)
> 
> Do we want to make sure that all the iec958 controls are on the same
> iface, or is it also left to the driver (or should we just leave the
> existing drivers as is but encourage a consistent use in the future)?

I'd leave the existing drivers as-is.  Changing the iface is basically
an incompatible change, and although most of applications and alsa-lib
should look at both ifaces, there can be any surprise by that change.


thanks,

Takashi