Re: [PATCH v4 4/4] watchdog: rzg2l_wdt: Power on the watchdog domain in the restart handler

[Andy Shevchenko <andriy.shevchenko@intel.com>]

On Tue, Oct 15, 2024 at 07:47:32PM +0300, Claudiu wrote:
> 
> On RZ/G3S the watchdog can be part of a software-controlled PM domain. In
> this case, the watchdog device need to be powered on in
> struct watchdog_ops::restart API. This can be done though
> pm_runtime_resume_and_get() API if the watchdog PM domain and watchdog
> device are marked as IRQ safe. We mark the watchdog PM domain as IRQ safe
> with GENPD_FLAG_IRQ_SAFE when the watchdog PM domain is registered and the
> watchdog device though pm_runtime_irq_safe().
> 
> Before commit e4cf89596c1f ("watchdog: rzg2l_wdt: Fix 'BUG: Invalid wait
> context'") pm_runtime_get_sync() was used in watchdog restart handler
> (which is similar to pm_runtime_resume_and_get() except the later one
> handles the runtime resume errors).
> 
> Commit e4cf89596c1f ("watchdog: rzg2l_wdt: Fix 'BUG: Invalid wait
> context'") dropped the pm_runtime_get_sync() and replaced it with
> clk_prepare_enable() to avoid invalid wait context due to genpd_lock()
> in genpd_runtime_resume() being called from atomic context. But
> clk_prepare_enable() doesn't fit for this either (as reported by
> Ulf Hansson) as clk_prepare() can also sleep (it just not throw invalid
> wait context warning as it is not written for this).

> Because the watchdog device is marked now as IRQ safe (though this patch)

...which is complete hack and has to be avoided.

Can it be solved differently? (Note, OMAP, for example, got patches in the past
and become pm_runtime_irq_safe()-free.)

> the irq_safe_dev_in_sleep_domain() call from genpd_runtime_resume() returns
> 1 for devices not registering an IRQ safe PM domain for watchdog (as the
> watchdog device is IRQ safe, PM domain is not and watchdog PM domain is
> always-on), this being the case for RZ/G3S with old device trees and
> the rest of the SoCs that use this driver, we can now drop also the
> clk_prepare_enable() calls in restart handler and rely on
> pm_runtime_resume_and_get().

> Thus, drop clk_prepare_enable() and use pm_runtime_resume_and_get() in
> watchdog restart handler.

-- 
With Best Regards,
Andy Shevchenko