[alsa-devel] [PATCH] ASoC: wm8741: Remove unneeded startup() callback

[Sergej Sawazki]

On Mon, 30 Jan 2017 09:22:59 +0000, Charles Keepax wrote:
> On Sat, Jan 28, 2017 at 12:35:45AM +0100, Sergej Sawazki wrote:
>> Do not apply rate constraints in the startup() callback. The machine driver
>> can change the sysclk and hence the supported frame rates in its hw_params().
>> This callback is unneeded since commit e369bd006fd6 ("ASoC: wm8741: Allow
>> master clock switching").

> This function should not be removed it is performing a useful
> function. If a sysclk has already been configured by the machine
> driver then we should inform user-space of the rates we can
> support from that clock. Without this that information is not
> available to user-space, so instead of user-space being able to
> resample appropriately it would just error out from hw_params.
> 
> Are you perhaps missing a call to clear the sysclk from your
> machine driver? Usually a dai_set_sysclk call with a rate of
> zero, also I find if it is a machine driver supporting multiple
> rates you are best to use ignore_pmdown_time on the DAI link,
> assuming the devices don't have long bring up times.

After clearing the sysclk, the codec should 'pretend' to support all
rates, right? (no sysclk -> no rate constrains)

After applying rate constraints using snd_pcm_hw_constraint_list(...),
what would be a clean way to remove the constraints from the rates
parameter?

Thanks,
Sergej