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

[Sameer Pujar]

On 1/25/2019 7:34 PM, Jon Hunter wrote:
> On 25/01/2019 13:58, Takashi Iwai wrote:
> > On Fri, 25 Jan 2019 14:26:27 +0100,
> > Jon Hunter wrote:
> > > On 25/01/2019 12:40, Takashi Iwai wrote:
> > > > 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@xxxxxxxxxx>
> > > > > > > Reviewed-by: Ravindra Lokhande <rlokhande@xxxxxxxxxx>
> > > > > > > Reviewed-by: Jon Hunter <jonathanh@xxxxxxxxxx>
> > > > > > (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.
> > > Yes and you can make the same argument for every driver that calls
> > > pm_runtime_get_sync() during probe to turn on clocks, handle resets,
> > > etc, because at the end of the day the very first call to
> > > pm_runtime_get_sync() invokes the runtime_resume callback, when we have
> > > never been suspended.
> > Although there are some magical pm_runtime_*() in some places, most of
> > such pm_runtime_get_sync() is for the actual runtime PM management (to
> > prevent the runtime suspend), while the code above is for explicitly
> > setting up something for non-PM cases.
> >
> > And if pm_runtime_get_sync() is obviously superfluous, we should
> > remove such calls.  Really.
> Yes agree.
>
> > > Yes at the end of the day it is the same and given that we have done
> > > this elsewhere I think it is good to be consistent if/where we can.
> > The code becomes less readable, and that's a good reason against it :)
> I don't its less readable. However, I do think it is less error prone :-)

Do we have a consensus here? Request others to provide opinions to help 
close on this.

Thanks,
Sameer.

> Jon