linux-kernel - Re: [PATCH RFC 3/3] watchdog: rzg2l_wdt: Power on the PM domain in rzg2l_wdt

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Message-ID: <CAPDyKFq1EX1Spedhkek=50EdwmHY5erNTmvegVGbxfLzTqYjEA@mail.gmail.com>
Date: Tue, 13 Aug 2024 15:56:24 +0200
From: Ulf Hansson <ulf.hansson@...aro.org>
To: Claudiu <claudiu.beznea@...on.dev>
Cc: wim@...ux-watchdog.org, linux@...ck-us.net, rafael@...nel.org, 
	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-watchdog@...r.kernel.org, geert+renesas@...der.be, 
	linux-renesas-soc@...r.kernel.org, 
	Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
Subject: Re: [PATCH RFC 3/3] watchdog: rzg2l_wdt: Power on the PM domain in rzg2l_wdt_restart()

On Wed, 19 Jun 2024 at 14:09, Claudiu <claudiu.beznea@...on.dev> wrote:
>
> From: Claudiu Beznea <claudiu.beznea.uj@...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?

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?

Kind regards
Uffe

>
> Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@...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
>