Re: [PATCH 19/19] ASoC: amd: ps: increase runtime suspend delay

[Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>]

On 1/12/23 09:29, Limonciello, Mario wrote:
> On 1/12/2023 08:54, Pierre-Louis Bossart wrote:
>>
>>
>> On 1/12/23 05:02, Mukunda,Vijendar wrote:
>>> On 11/01/23 21:32, Pierre-Louis Bossart wrote:
>>>> On 1/11/23 03:02, Vijendar Mukunda wrote:
>>>>> To avoid ACP entering into D3 state during slave enumeration and
>>>>> initialization on two soundwire controller instances for multiple
>>>>> codecs,
>>>>> increase the runtime suspend delay to 3 seconds.
>>>> You have a parent PCI device and a set of child devices for each
>>>> manager. The parent PCI device cannot suspend before all its children
>>>> are also suspended, so shouldn't the delay be modified at the
>>>> manager level?
>>>>
>>>> Not getting what this delay is and how this would deal with a lengthy
>>>> enumeration/initialization process.
>>> Yes agreed. Until Child devices are suspended, parent device will
>>> be in D0 state. We will rephrase the commit message.
>>>
>>> Machine driver node will be created by ACP PCI driver.
>>> We have added delay in machine driver to make sure
>>> two manager instances completes codec enumeration and
>>> peripheral initialization before registering the sound card.
>>> Without adding delay in machine driver will result early card
>>> registration before codec initialization is completed. Manager
>>> will enter in to bad state due to codec read/write failures.
>>> We are intended to keep the ACP in D0 state, till sound card
>>> is created and jack controls are initialized. To handle, at manager
>>> level increased runtime suspend delay.
>>
>> This doesn't look too good. You should not assume any timing
>> dependencies in the machine driver probe. I made that mistake in earlier
>> versions and we had to revisit all this to make sure drivers could be
>> bound/unbound at any time.
> 
> Rather than a timing dependency, could you perhaps prohibit runtime PM
> and have a codec make a callback to indicate it's fully initialized and
> then allow runtime PM again?

We already have enumeration and initialization 'struct completion' that
are used by codec drivers to know if the hardware is usable. We also
have pm_runtime_get_sync() is the bus layer to make sure the codec is
resumed before being accessed.

The explanations above confuse card registration and manager
probe/initialization. These are two different things. Maybe there's
indeed a missing part in the SoundWire PM assumptions, but I am not
getting what the issue is.