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

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Message-ID: <s5hlg9sr9c8.wl-tiwai@suse.de>
Date:   Mon, 30 Jul 2018 18:12:39 +0200
From:   Takashi Iwai <tiwai@...e.de>
To:     Jorge <jorge.sanjuan@...ethink.co.uk>
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 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.


thanks,

Takashi