linux-kernel - Re: [PATCH RESEND v8 09/10] watchdog: rzg2l_wdt: Power on the PM domain in rzg2l_wdt

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Message-ID: <CAPDyKFq1+cL1M9qGY0P58ETHUZHGymxQL0w92emUJPMe7a_GxA@mail.gmail.com>
Date: Fri, 12 Apr 2024 13:18:51 +0200
From: Ulf Hansson <ulf.hansson@...aro.org>
To: Claudiu <claudiu.beznea@...on.dev>
Cc: wim@...ux-watchdog.org, linux@...ck-us.net, robh@...nel.org, 
	krzk+dt@...nel.org, conor+dt@...nel.org, p.zabel@...gutronix.de, 
	geert+renesas@...der.be, magnus.damm@...il.com, biju.das.jz@...renesas.com, 
	linux-watchdog@...r.kernel.org, devicetree@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-renesas-soc@...r.kernel.org, 
	Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
Subject: Re: [PATCH RESEND v8 09/10] watchdog: rzg2l_wdt: Power on the PM
 domain in rzg2l_wdt_restart()

On Wed, 10 Apr 2024 at 16:19, Claudiu <claudiu.beznea@...on.dev> wrote:
>
> From: Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
>
> The rzg2l_wdt_restart() is called from 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 used directly the
> clk_prepare_enable() APIs.

Calling clk_prepare_enable() doesn't work from an atomic context
either as it may sleep on the clk prepare mutex.

As I said in the other reply too, it looks like we need a different
solution. I am not sure what, but I am happy to help discuss it.

>
> Starting with RZ/G3S the watchdog could be part of its own software
> controlled power domain (see the initial implementation in Link section).
> 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() API before enabling its clock. This is not
> sleeping or taking any other locks as the power domain will not be
> registered with GENPD_FLAG_IRQ_SAFE flags.
>
> Link: https://lore.kernel.org/all/20240208124300.2740313-1-claudiu.beznea.uj@bp.renesas.com
> Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@...renesas.com>

Kind regards
Uffe

> ---
>
> Changes in v8:
> - none, this patch is new
>
>  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 c8c20cfb97a3..98e5e9914a5d 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>
> @@ -164,6 +165,17 @@ static int rzg2l_wdt_restart(struct watchdog_device *wdev,
>         struct rzg2l_wdt_priv *priv = watchdog_get_drvdata(wdev);
>         int ret;
>
> +       /*
> +        * The device may be part of a power domain that is currently
> +        * powered off. We need to power it up before accessing registers.
> +        * We don't undo the dev_pm_genpd_resume() as the device need to
> +        * be up 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(wdev->parent);
> +
>         clk_prepare_enable(priv->pclk);
>         clk_prepare_enable(priv->osc_clk);
>
> --
> 2.39.2
>
>