Re: [PATCH v2 1/1] mmc: sdhci-omap: Fix a lockdep warning for PM runtime init

[Tony Lindgren <tony@atomide.com>]

* Ulf Hansson <ulf.hansson@linaro.org> [220712 09:52]:
> On Mon, 27 Jun 2022 at 08:13, Tony Lindgren <tony@atomide.com> wrote:
> >
> > * Ulf Hansson <ulf.hansson@linaro.org> [220623 12:55]:
> > > On Wed, 22 Jun 2022 at 07:12, Tony Lindgren <tony@atomide.com> wrote:
> > > >
> > > > We need runtime PM enabled early in probe before sdhci_setup_host() for
> > > > sdhci_omap_set_capabilities(). But on the first runtime resume we must
> > > > not call sdhci_runtime_resume_host() as sdhci_setup_host() has not been
> > > > called yet. Let's check for an initialized controller like we already do
> > > > for context restore to fix a lockdep warning.
> > >
> > > Thanks for explaining the background to the problem. However, looking
> > > a bit closer I am worried that the error path in ->probe() is broken
> > > too.
> > >
> > > It seems in the error path, at the label "err_rpm_put", there is a
> > > call to pm_runtime_put_autosuspend(). This doesn't really guarantee
> > > that the ->runtime_suspend() callback will be invoked, which I guess
> > > is the assumption, don't you think?
> >
> > OK I'll check and send a separate patch for that.
> >
> > > That said, I wonder if it would not be easier to convert the ->probe()
> > > function to make use of pm_runtime_get_noresume() and
> > > pm_runtime_set_active() instead. In this way the ->probe() function
> > > becomes responsible of turning on/off the resources "manually" that it
> > > requires to probe (and when it fails to probe), while we can keep the
> > > ->runtime_suspend|resume() callbacks simpler.
> > >
> > > Did that make sense to you?
> >
> > Simpler would be better :) We need to call pm_runtime_get_sync() at some
> > point though to enable the parent device hierarchy.
> 
> Is there a parent device that has runtime PM enabled?

Yes there is the interconnect target module device as the parent with
runtime PM enabled. So the sdhci-omap driver needs the parent enabled.

> In other cases, it should be fine to use pm_runtime_set_active()
> during ->probe().

Yup, this can't be done here though AFAIK. Something needs to enable
runtime PM for the parent device to have the sdhci registers accessible.

> > Just calling the
> > sdhci_omap runtime functions is not enough. And we still need to check
> > for the valid context too. Also I'm not convinced that calling
> > pm_runtime_get_sync() on the parent device would do the right thing on
> > old omap3 devices without bigger changes..
> 
> I certainly agree. The parent should not be managed directly by the
> sdhci driver.

OK

> One thing that can be discussed though, is whether
> pm_runtime_set_active() actually should runtime resume the parent,
> which would make the behaviour consistent with how suppliers are being
> treated.

Hmm yeah that's an interesting idea.

> > But maybe you have some better
> > ideas that I'm not considering.
> 
> I can try to draft a patch, if that would help? But, let's finalize
> the discussion above first (apologize for the delay).

OK. Should we apply the $subject patch to fix the splat meanwhile
though? Seems like what you're suggesting may take some more discussion
on the mailing lists.

Regrads,

Tony