linux-kernel - Re: [alsa-devel] [PATCH 1/2 v2] ASoC: sh: fsi: Add runtime PM support

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Date:	Mon, 9 Nov 2009 10:58:58 +0000
From:	Mark Brown <broonie@...nsource.wolfsonmicro.com>
To:	Kuninori Morimoto <morimoto.kuninori@...esas.com>
Cc:	alsa-devel@...a-project.org, Magnus Damm <damm@...l.co.jp>,
	"Rafael J. Wysocki" <rjw@...k.pl>, linux-kernel@...r.kernel.org
Subject: Re: [alsa-devel] [PATCH 1/2 v2] ASoC: sh: fsi: Add runtime PM
	support

On Mon, Nov 09, 2009 at 11:54:47AM +0900, Kuninori Morimoto wrote:
> This patch add support runtime PM.
> Driver callbacks for Runtime PM are empty because
> the device registers are always re-initialized after
> pm_runtime_get_sync(). The Runtime PM functions replaces the
> clock framework module stop bit handling in this driver.

> Signed-off-by: Kuninori Morimoto <morimoto.kuninori@...esas.com>

Hrm.  I'll have to see how this plays with ASoC core pm_runtime support
when that appears.  It should be OK as-is, I think.

> +	pm_suspend_ignore_children(&pdev->dev, true);
> +	pm_runtime_enable(&pdev->dev);
> +	pm_runtime_resume(&pdev->dev);

Why pm_suspend_ignore_all_children()?  I'd not expect the device to have
any children and if it did it doesn't seem like an entirely safe
assumption.

> +static int fsi_runtime_nop(struct device *dev)
> +{
> +	/* Runtime PM callback shared between ->runtime_suspend()
> +	 * and ->runtime_resume(). Simply returns success.
> +	 *
> +	 * This driver re-initializes all registers after
> +	 * pm_runtime_get_sync() anyway so there is no need
> +	 * to save and restore registers here.
> +	 */
> +	return 0;
> +}

This sets off alarm bells but it's perfectly reasonable, especially with
platforms able to put things into a low power state with no explicit
driver code now they can do power domain style things like SH.  I've
CCed in the PM folks since this seems like a perfectly reasonable use
case which ought to be handled more nicely.
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