[alsa-devel] [PATCHv2 5/7] ASoC: TWL6030: Add support for low-power mode

[Lopez Cruz, Misael]

Mark,

Mark Brown wrote:
> On Fri, Sep 25, 2009 at 09:03:30PM -0500, Lopez Cruz, Misael wrote:
>> In high-performance mode, codec can only work at 19.2 MHz from
>> high-performance PLL. All paths supported in the codec can be used
>> but audio can be streamed only at 48 kHz.

> The driver should also set constraints at runtime so that applications
> know they shouldn't use an unsupported sample rate.  See wm8988 for an
> example of doing this - it has some similar SYSCLK based restrictions.

In OMAP4, we can have the processor connected to Audio Backend and
then to Phoenix (OMAP4->ABE->McPDM->TWL6030), but it's also possible
to bypass the Audio Backend (OMAP4->McPDM->TWL6030).

The McPDM link requires data to be sent at twice the desired rate.
In the first scenario (Audio Backend enabled), OMAP4 sends the data
at 48kHz to ABE and it upsamples it to 96kHz and then send to TWL6030
through McPDM. In the second scenario (Audio Backend bypassed),
OMAP4 has to send the audio data at 96kHz, since no upsampling
blocks are available now.