[alsa-devel] [PATCH v2] ASoC: rt5670: add clock source selection controls

[Mark Brown]

On Tue, Sep 02, 2014 at 05:22:49AM +0000, Bard Liao wrote:

> Which clock source should be selected mainly decided by the sampling
> rate and the audio routing path. However, there are some exceptions.
> For example, if the MCLK and I2S clock are asynchronous, we should
> always select "clk_i2s_track" as the clock source. And In some cases,
> we can choice "clk_i2s_track" or "clk_sysy_div_out" as the clock source.
> Users can choose what they want to use.

> Even if we ignore all the exceptions and make choice for users, it is still
> hard to implement it in the driver since we need to read a lot of registers
> to decide the clock source. It will be easier if we open it to user space
> so user can configure it with the audio routing path.

The choice is usually deferred to the machine driver rather than made
entirely automatically within the CODEC driver - where manual control is
required typically the machine driver is then able to offer a bigger,
system-wide choice to the user that controls several settings and makes
sure that any required coordination occurs.
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