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

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Date:   Fri, 25 Jan 2019 13:40:37 +0100
From:   Takashi Iwai <tiwai@...e.de>
To:     Jon Hunter <jonathanh@...dia.com>
Cc:     Sameer Pujar <spujar@...dia.com>,
        <pierre-louis.bossart@...ux.intel.com>, <perex@...ex.cz>,
        <alsa-devel@...a-project.org>, <thierry.reding@...il.com>,
        <rlokhande@...dia.com>, <linux-kernel@...r.kernel.org>,
        <linux-tegra@...r.kernel.org>
Subject: Re: [PATCH] ALSA: hda/tegra: enable clock during probe

On Fri, 25 Jan 2019 12:36:00 +0100,
Jon Hunter wrote:
> 
> 
> On 24/01/2019 19:08, Takashi Iwai wrote:
> > On Thu, 24 Jan 2019 18:36:43 +0100,
> > Sameer Pujar wrote:
> >>
> >> If CONFIG_PM is disabled or runtime PM calls are forbidden, the clocks
> >> will not be ON. This could cause issue during probe, where hda init
> >> setup is done. This patch checks whether runtime PM is enabled or not.
> >> If disabled, clocks are enabled in probe() and disabled in remove()
> >>
> >> This patch does following minor changes as cleanup,
> >>   * return code check for pm_runtime_get_sync() to take care of failure
> >>     and exit gracefully.
> >>   * In remove path runtime PM is disabled before calling snd_card_free().
> >>   * hda_tegra_disable_clocks() is moved out of CONFIG_PM_SLEEP check.
> >>   * runtime PM callbacks moved out of CONFIG_PM check
> >>
> >> Signed-off-by: Sameer Pujar <spujar@...dia.com>
> >> Reviewed-by: Ravindra Lokhande <rlokhande@...dia.com>
> >> Reviewed-by: Jon Hunter <jonathanh@...dia.com>
> > (snip)
> >> @@ -555,6 +553,13 @@ static int hda_tegra_probe(struct platform_device *pdev)
> >>  	if (!azx_has_pm_runtime(chip))
> >>  		pm_runtime_forbid(hda->dev);
> >>  
> >> +	/* explicit resume if runtime PM is disabled */
> >> +	if (!pm_runtime_enabled(hda->dev)) {
> >> +		err = hda_tegra_runtime_resume(hda->dev);
> >> +		if (err)
> >> +			goto out_free;
> >> +	}
> >> +
> >>  	schedule_work(&hda->probe_work);
> > 
> > Calling runtime_resume here is really confusing...
> 
> Why? IMO it is better to have a single handler for resuming the device
> and so if RPM is not enabled we call the handler directly. This is what
> we have been advised to do in the past and do in other drivers. See ...

The point is that we're not "resuming" anything there.  It's in the
early probe stage, and the device state is uninitialized, not really
suspended.  It'd end up with just calling the same helper
(hda_tegra_enable_clocks()), though.


Takashi