Re: [PATCH 06/13] ASoC: tegra: Add Tegra210 based MVC driver

[Sameer Pujar <spujar@nvidia.com>]

On 9/7/2021 1:35 PM, Sameer Pujar wrote:
> On 9/3/2021 11:43 PM, Mark Brown wrote:
>> On Fri, Aug 27, 2021 at 03:03:52PM +0530, Sameer Pujar wrote:
>
>>> +	/* SW reset */
>>> +	regmap_write(mvc->regmap, TEGRA210_MVC_SOFT_RESET, 1);
>> What about all the cached values in the regmap, won't they get out of
>> sync?  Especially things like volume and mute, it looks like the mute
>> just gets written directly to the regmap and not otherwise saved.
>
> 1. I think original idea was to disable MVC (forcefully) before new 
> configurations are applied and eventually it gets enabled via DAPM 
> path. DAPM path handles disable also, but sometimes MVC may get stuck 
> in enable state (due to a previous usage) when all the data in 
> pipeline is not processed. My understanding is that reset is 
> restricted to this alone. The volume/mute registers seem not to be 
> affected by reset. However I will confirm with HW about the reset 
> behavior and affected register map. Thanks for pointing this.
>

I confirmed the behavior with HW folk here. The reset above clears all 
FSM, flushes flow control of FIFO and resets the state registers. It 
also brings module back to disabled state (without flushing the data in 
the pipe). There is no impact on the register cache, as state registers 
are anyway volatile and module disable is applicable only when it was 
hung in previous usage. Otherwise DAPM would disable the module during 
session close.