Re: [PATCH] serial: 8250_omap: Set the console genpd always on if no console suspend

[Tony Lindgren <tony@atomide.com>]

* Kevin Hilman <khilman@kernel.org> [231024 18:36]:
> Tony Lindgren <tony@atomide.com> writes:
> 
> > * Kevin Hilman <khilman@kernel.org> [231023 21:31]:
> >> Instead, what should be happening is that when `no_console_suspend` is
> >> set, there should be an extra pm_runtime_get() which increases the
> >> device usecount such that the device never runtime suspends, and thus
> >> the domain will not get powered off.
> >
> > We already have the runtime PM usage count kept in the driver (unless
> > there's a bug somewhere). The issue is that on suspend the power domain
> > still gets shut down.
> >
> > I suspect that some of the SoC power domains get
> > force shut down on suspend somewhere?
> 
> If setting GENPD_FLAG_ALWAYS_ON works as this patch proposes, then a
> force shutdown would override that genpd flag also, so I suspect the 
> runtime PM usage count is not correct.

OK good point.

> I quick skim of 8250_omap.c, and I don't see any pm_runtime_get() calls
> that are conditional on no_console_suspend, which is what I would
> suspect for the domain to stay on.

If a serial console is attached, we now have runtime PM usage count
always kept. Users can detach the console via sysfs as needed. See these
two earlier commits from Andy:

a3cb39d258ef ("serial: core: Allow detach and attach serial device for console")
bedb404e91bb ("serial: 8250_port: Don't use power management for kernel console")

Sounds like there's a bug somewhere. It's worth verifying if the runtime
PM usage count is kept for 8250_omap on suspend.

Thomas, care to check your test case with the attached debug hack
and by adding a call for pm_runtime_get_usage_count() on the suspend
path?

Regards,

Tony

8< -------------------------------
diff --git a/include/linux/pm_runtime.h b/include/linux/pm_runtime.h
--- a/include/linux/pm_runtime.h
+++ b/include/linux/pm_runtime.h
@@ -129,6 +129,11 @@ static inline void pm_runtime_get_noresume(struct device *dev)
 	atomic_inc(&dev->power.usage_count);
 }
 
+static inline int pm_runtime_get_usage_count(struct device *dev)
+{
+	return atomic_read(&dev->power.usage_count);
+}
+
 /**
  * pm_runtime_put_noidle - Drop runtime PM usage counter of a device.
  * @dev: Target device.