linux-kernel - Re: [PATCH v2 4/4] ALSA: usb-audio: Operate UAC3 Power Domains in PCM callbacks

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Message-ID: <88a51510-598d-3a95-ab29-138ff317312e@codethink.co.uk>
Date:   Mon, 30 Jul 2018 17:48:40 +0100
From:   Jorge <jorge.sanjuan@...ethink.co.uk>
To:     Takashi Iwai <tiwai@...e.de>
Cc:     alsa-devel@...a-project.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 4/4] ALSA: usb-audio: Operate UAC3 Power Domains in PCM
 callbacks



On 30/07/18 17:12, Takashi Iwai wrote:
> On Mon, 30 Jul 2018 18:09:38 +0200,
> Jorge wrote:
>>
>>
>>
>> On 30/07/18 14:13, Takashi Iwai wrote:
>>> On Mon, 30 Jul 2018 11:23:36 +0200,
>>> Jorge Sanjuan wrote:
>>>>
>>>> Make use of UAC3 Power Domains associated to an Audio Streaming
>>>> path within the PCM's logic. This means, when there is no audio
>>>> being transferred (pcm is closed), the host will set the Power Domain
>>>> associated to that substream to state D1. When audio is being transferred
>>>> (from hw_params onwards), the Power Domain will be set to D0 state.
>>>>
>>>> This is the way the host lets the device know which Terminal
>>>> is going to be actively used and it is for the device to
>>>> manage its own internal resources on that UAC3 Power Domain.
>>>>
>>>> Note the resume method now sets the Power Domain to D1 state as
>>>> resuming the device doesn't mean audio streaming will occur.
>>>
>>> I guess we need the power state transition to D0 also in prepare
>>> callback.  The recovery from suspend doesn't need hw_params call but
>>> just prepare -> trigger.
>>
>> Right! Shouldn't it then be enough to just go to D0 on .prepare? I,e.
>> Move the state transition from .hw_params to .prepare.
> 
> Does the power domain transition needed for setting the format, EP,
> etc done in set_format()?  If yes, we need D0 in hw_parmas as well.

Ok. That's a good point. The Power Domain will affect the USB streaming
terminals so a device may implement this in a way so it is not capable
to set_formats properly. I'll make sure the Power Domain is always set
to D0 *before* attempting to set_format.

Thanks!

Jorge

> 
> 
> thanks,
> 
> Takashi
>