[alsa-devel] [Patch V4 03/10] ASoC: qcom: Document LPASS CPU bindings

[Kenneth Westfield]

On Sat, Feb 07, 2015 at 06:18:23AM +0800, Mark Brown wrote:
> On Thu, Feb 05, 2015 at 12:53:39PM -0800, Kenneth Westfield wrote:
> 
> > +- qcom,system-clock-shift		: Add this bool property if the default
> > +					  frequency of the system clock needs to
> > +					  be reduced.
> > +- qcom,system-clock-shift-compare	: A numerical value used to right-shift
> > +					  the default system clock frequency for
> > +					  comparison with the target bit clock
> > +					  frequency.
> > +- qcom,system-clock-shift-amount	: A numerical value used to right-shift
> > +					  the default system clock frequency.
> > +- qcom,alternate-sysclk			: Add this bool property if the default
> > +					  frequency of the system clock cannot
> > +					  divide down to the target bit clock
> > +					  frequency.
> > +- qcom,alternate-sysclk-bitwidth	: A numerical value representing the
> > +					  sample bitwidth which requires use of
> > +					  the alternate system clock frequency.
> > +- qcom,alternate-sysclk-frequency	: A numerical value representing the new
> > +					  system clock frequency to use.
> 
> None of these seem like they are appropriate for device tree properties,
> they appear to be choosing a specific clocking configuration which is
> something that would normally be done as part of the system integration
> in the machine driver rather than in the DAI driver.  This binding won't
> work in cases where the clocks are being changed at runtime and would
> limit systems where that becomes possible in future.

So I add a machine driver that selects the clocking freq in hw_params
and calls set_sysclk in the DAIs.

The DT node for the machine driver would look something like:
        default_system_clock_frequency = < xxxxxx >;
        alternate_system_clock_frequency = < xxxxxx >;
        cpu_dai = < &cpu >;
        codec_dai = < &codec >;
        pinctrl... ?

Does this sound ok?  Also, would it make sense to move the pinctrl back
to the machine driver?

-- 
Kenneth Westfield
Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, 
a Linux Foundation Collaborative Project