Re: [alsa-devel] [RFC PATCH 28/40] soundwire: intel: handle disabled links

[Pierre-Louis Bossart]

On 8/5/19 11:57 AM, Sanyog Kale wrote:
> On Thu, Jul 25, 2019 at 06:40:20PM -0500, Pierre-Louis Bossart wrote:
> > On most hardware platforms, SoundWire interfaces are pin-muxed with
> > other interfaces (typically DMIC or I2S) and the status of each link
> > needs to be checked at boot time.
> >
> > For Intel platforms, the BIOS provides a menu to enable/disable the
> > links separately, and the information is provided to the OS with an
> > Intel-specific _DSD property. The same capability will be added to
> > revisions of the MIPI DisCo specification.

[snip]

> > diff --git a/include/linux/soundwire/sdw.h b/include/linux/soundwire/sdw.h
> > index c7dfc824be80..f78b076a8782 100644
> > --- a/include/linux/soundwire/sdw.h
> > +++ b/include/linux/soundwire/sdw.h
> > @@ -380,6 +380,7 @@ struct sdw_slave_prop {
> >    * @err_threshold: Number of times that software may retry sending a single
> >    * command
> >    * @mclk_freq: clock reference passed to SoundWire Master, in Hz.
> > + * @hw_disabled: if true, the Master is not functional, typically due to pin-mux
> >    */
> >   struct sdw_master_prop {
> >   	u32 revision;
> > @@ -395,6 +396,7 @@ struct sdw_master_prop {
> >   	bool dynamic_frame;
> >   	u32 err_threshold;
> >   	u32 mclk_freq;
> > +	bool hw_disabled;
>
> Do we have such cases where some of SoundWire links are disabled and
> some enabled?

Yes, by default my ICL test board uses HDaudio for the codec so the 
SoundWire link0 is disabled. If I rework the board and change the BIOS 
advanced menu then SoundWire link0 is enabled. This information is 
dynamically provided to the OS after the _INI step.
SoundWire-2/3 are used typically for attached DMICs or for a combination 
of SoundWire amplifier and mic capture. It's really platform-specific.

> >   };
> >   
> >   int sdw_master_read_prop(struct sdw_bus *bus);
> > --
> > 2.20.1