linux-kernel - Re: [PATCH v2] ALSA: hda/tegra: enable clock during probe

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Date:   Mon, 04 Feb 2019 11:13:49 +0100
From:   Takashi Iwai <tiwai@...e.de>
To:     Jon Hunter <jonathanh@...dia.com>
Cc:     Sameer Pujar <spujar@...dia.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Thierry Reding <thierry.reding@...il.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>,
        Jaroslav Kysela <perex@...ex.cz>,
        "moderated list:SOUND - SOC LAYER / DYNAMIC AUDIO POWER MANAGEM..." 
        <alsa-devel@...a-project.org>, <mkumard@...dia.com>,
        <rlokhande@...dia.com>, <sharadg@...dia.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        <linux-tegra@...r.kernel.org>, Linux PM <linux-pm@...r.kernel.org>
Subject: Re: [PATCH v2] ALSA: hda/tegra: enable clock during probe

On Mon, 04 Feb 2019 11:04:50 +0100,
Jon Hunter wrote:
> 
> 
> On 04/02/2019 08:16, Sameer Pujar wrote:
> 
> ...
> 
> > Objective is to have things working with or without CONFIG_PM enabled.
> > From previous comments and discussions it appears that there is mixed
> > response
> > for calling hda_tegra_runtime_resume() or runtime PM APIs in probe()
> > call. Need
> > to have consensus regarding the best practice to be followed, which
> > would eventually
> > can be used in other drivers too.
> > 
> > Rafael is suggesting to use CONFIG_PM check to do manual setup or
> > runtime PM setup in probe,
> > which would bring back the earlier above mentioned concern.
> > 
> > if (IS_ENABLED(CONFIG_PM)) {
> > do setup based on pm-runtime
> > } else {
> >     do manual setup
> > }
> > Both if/else might end up doing the same here.
> > Do we really need CONFIG_PM check here?
> > 
> > Instead does below proposal appear fine?
> > 
> > probe() {
> >     hda_tegra_enable_clock();
> > }
> > 
> > probe_work() {
> >     /* hda setup */
> >     . . .
> >     pm_runtime_set_active(); /* initial state as active */
> >     pm_runtime_enable();
> >     return;
> > }
> 
> I believe that this still does not work, because if there is a
> power-domain that needs to be turned on, this does not guarantee this.
> So I think that you need to call pm_runtime_get ...
> 
>  probe() {
>  	if (!IS_ENABLED(CONFIG_PM))
>  		hda_tegra_enable_clock();
>  }
> 
> 
>  probe_work() {
>     	/* hda setup */
>     	. . .
> 	pm_runtime_enable();
> 	pm_runtime_get_sync();
> 	return;
>  }
> 
> The alternative here could just be ...
> 
>  probe() {
> 	pm_runtime_enable();
>  	if (!pm_runtime_enabled())
>  		ret = hda_tegra_enable_clock();
> 	else
> 		ret = pm_runtime_get_sync();
> 
> 	if (ret < 0) {
> 		...
> 	}
>  }
> 
> Very similar to what I was saying to begin with but not call the
> pm_runtime_resume handler directly. Which I believe was Iwai-san's dislike.

Yes, exactly, what bothered me was really a nuance: calling
hda_tegra_runtime_resume() there makes the code misleading (or
confusing) as if the runtime PM were mandatory.

I hoped there could be some standard idiom for this expression, but
apparently there isn't any, so far...

Obviously the easiest option is to enforce the dependency on
CONFIG_PM.  Would there be any platform that needs to run without PM,
practically seen...?

But, now after lengthy discussions and the clarification of the
current situation, I have no strong opinion on this any longer.
So I leave the decision to you guys, and I'll apply it as-is.


thanks,

Takashi