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

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Message-ID: <s5h8t5sx3x9.wl-tiwai@suse.de>
Date:   Mon, 30 Jul 2018 15:13:06 +0200
From:   Takashi Iwai <tiwai@...e.de>
To:     Jorge Sanjuan <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 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.

One could think of implementing into the trigger, but since the
transition needs some delay, prepare callback would be a better
choice, as it seems.


thanks,

Takashi