[alsa-devel] [PATCH 17/31] ASoC: tegra: call pm_runtime APIs around register accesses

[Stephen Warren]

On 11/16/2013 03:02 AM, Mark Brown wrote:
> On Fri, Nov 15, 2013 at 01:54:12PM -0700, Stephen Warren wrote:
>> From: Stephen Warren <swarren at nvidia.com>
>>
>> Call pm_runtime_get_sync() before all register accesses; the HW requires
>> clocks to be running when accessing registers.
>>
>> This hasn't been needed to date, since all register IO was performed
>> while playback was active, and hence the ASoC core had already called
>> pm_runtime_get(). However, an imminent future commit will allocate and
>> set up the FIFOs and routing during probe(), when that "protection"
>> won't be in place.
> 
> Acked-by: Mark Brown <broonie at linaro.org>
> 
> However should we fix this at the regmap level in the same way that we
> do for clocks?  That would need to be using _put_autosuspend() to avoid
> being horrific.

I did wonder about that, but it seemed like rather a lot of overhead?

> Or alternatively should the driver be making the device
> cache only when runtime PM is disabled?

The regmap is already cache-only when runtime-suspended. However the
registers don't get flushed during resume. I suppose that would require
only adding one extra call to the PM resume function?

For some reason, my gut prefers this current solution, but I could be
persuaded.