[alsa-devel] [PATCH] ASoC: adau1701: Reset codec based on sample rate changes

[Pascal Huerst]

On 23.03.2016 14:44, Lars-Peter Clausen wrote:
> On 03/23/2016 12:58 PM, pascal.huerst at gmail.com wrote:
>> From: Pascal Huerst <pascal.huerst at gmail.com>
>>
>> Instead of checking if mclk/lrclk ratio has changed, check if
>> sample rate has changed. In certain cases, the mclk might be
>> changed in the machine driver, which can lead to the same
>> mclk/lrclk ration, eventhow the sample rate has changed.
>>
>> Since the codec has to be programmed differently for every
>> sample rate, its better to check for samplerate changes instead
>> of mclk/lrclk ration changes.
> 
> Mark's comment made me give this some additional though. Do we actually
> need to reset the device if the clkdiv did not change. Stopping the DSP,
> uploading the new firmware and then restarting it should be sufficient.
> But on the other hand the time the reset takes should be negligible
> compared to programming the firmware, so it might be ok to always do it.
> Let me know what you think.

Ok, I see your point. So I did some measurements.

On our devices,

a firmware download takes about: 844ms
Resetting the pll settings takes about: 87ms

I'm not sure, if this worth the effort, but certainly it could be done.
I would probably leave it for now, be a bit more precise in the comment
above and add a note to the commit message, as Mark suggested (?)

While at it I also saw, that we should keep the reset line low, while
changing the pll settings. (Which we don't right now)

The datasheet states:

... "The state of the PLL_MODEx pins should be changed while RESET is
held low." ...