Re: [PATCH RFC 3/3] watchdog: rzg2l_wdt: Power on the PM domain in rzg2l_wdt_restart()

[claudiu beznea <claudiu.beznea@tuxon.dev>]

Hi, Ulf,

Sorry for the late reply, I was off last week.

On 13.08.2024 16:56, Ulf Hansson wrote:
> On Wed, 19 Jun 2024 at 14:09, Claudiu <claudiu.beznea@tuxon.dev> wrote:
>>
>> From: Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com>
>>
>> The rzg2l_wdt_restart() is called in atomic context. Calling
>> pm_runtime_{get_sync, resume_and_get}() or any other runtime PM resume
>> APIs is not an option as it may lead to issues as described in commit
>> e4cf89596c1f ("watchdog: rzg2l_wdt: Fix 'BUG: Invalid wait context'")
>> that removed the pm_runtime_get_sync() and enabled directly the clocks.
>>
>> Starting with RZ/G3S the watchdog could be part of its own
>> software-controlled power domain. In case the watchdog is not used the
>> power domain is off and accessing watchdog registers leads to aborts.
>>
>> To solve this, the patch powers on the power domain using
>> dev_pm_genpd_resume_restart_dev() API after enabling its clock. This is
>> not sleeping or taking any other locks as the watchdog power domain is not
>> registered with GENPD_FLAG_IRQ_SAFE flags.
> 
> Would it be a problem to register the corresponding genpd using the
> GENPD_FLAG_IRQ_SAFE?

Should be no problem, AFIK.

> 
> Assuming it wouldn't, it looks like we should be able to make the
> watchdog device irq-safe too, by calling pm_runtime_irq_safe() during
> ->probe().
> 
> In that case it should be okay to call pm_runtime_get_sync() in atomic
> context, right?

Right! I registered the watchdog domain with GENPD_FLAG_IRQ_SAFE as well as
it's parent domain (the always-on domain) and all looks good. However I
need to run further testing to be sure nothing is broken.

Thank you,
Claudiu Beznea

> 
> Kind regards
> Uffe
> 
>>
>> Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com>
>> ---
>>  drivers/watchdog/rzg2l_wdt.c | 12 ++++++++++++
>>  1 file changed, 12 insertions(+)
>>
>> diff --git a/drivers/watchdog/rzg2l_wdt.c b/drivers/watchdog/rzg2l_wdt.c
>> index 6e3d7512f38c..bbdbbaa7b82b 100644
>> --- a/drivers/watchdog/rzg2l_wdt.c
>> +++ b/drivers/watchdog/rzg2l_wdt.c
>> @@ -12,6 +12,7 @@
>>  #include <linux/module.h>
>>  #include <linux/of.h>
>>  #include <linux/platform_device.h>
>> +#include <linux/pm_domain.h>
>>  #include <linux/pm_runtime.h>
>>  #include <linux/reset.h>
>>  #include <linux/units.h>
>> @@ -169,6 +170,17 @@ static int rzg2l_wdt_restart(struct watchdog_device *wdev,
>>         clk_enable(priv->pclk);
>>         clk_enable(priv->osc_clk);
>>
>> +       /*
>> +        * The device may be part of a power domain that is currently
>> +        * powered off. We need to power it on before accessing registers.
>> +        * We don't undo the dev_pm_genpd_resume_restart_dev() as the device
>> +        * need to be on for the reboot to happen. Also, as we are in atomic
>> +        * context here, there is no need to increment PM runtime usage counter
>> +        * (to make sure pm_runtime_active() doesn't return wrong code).
>> +        */
>> +       if (!pm_runtime_active(wdev->parent))
>> +               dev_pm_genpd_resume_restart_dev(wdev->parent);
>> +
>>         if (priv->devtype == WDT_RZG2L) {
>>                 ret = reset_control_deassert(priv->rstc);
>>                 if (ret)
>> --
>> 2.39.2
>>