[alsa-devel] [PATCH v2] ASoC: Intel: Add Cherrytrail & Braswell machine driver cht_bsw_rt5672

[Lin, Mengdong]

+ Liam.

> -----Original Message-----
> From: Mark Brown [mailto:broonie at kernel.org]
> Sent: Wednesday, October 29, 2014 6:31 PM

> > > Nothing ever stops the PLL - a set_bias_level() callback with a handler for
> _OFF.
> > > Otherwise we're wasting power.
> 
> > Can we introduce a power supply widget for the platform clock used as
> MCLK?
> > That widget can be added into the playback and capture path.
> > So when idle, the platform clock can be turn off and let the codec PLL
> > selects its internal low frequency clock only for jack detection. It's verified
> internally.
> 
> That should be fine also, it's just usually a bit more work to add all the routes
> for DAPM.
> 
> > Or we don't change the code at moment, until we upstream the platform
> > clock driver at first?
> 
> > Which way is better?
> 
> Well, currently the code to load the driver is also not upstream so may as well
> have the driver be what's wanted!  But it's not a massive deal, main thing
> would be to get everything done as part of initial upstreaming instead of
> having to come back and work on it again later.

Now we're working with Realtek to enable runtime PM on RT5672 codec driver.
With help of ACPI, 
- the codec will be in suspended to D3 when idle , switch to its internal clock, 
 and BIOS will turn off the platform clock output (MCLK) to save power.
- And when the codec resumes to D0, BIOS will turn on the clock at first. And 
 hw_params will make the codec use PLL and lock to MCLK again.

Thus the machine driver does not need to explicitly turn on/off the platform 
codec by itself.

Thanks
Mengdong