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

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Date: Wed, 10 Apr 2024 09:43:14 -0700
From: Guenter Roeck <linux@...ck-us.net>
To: Claudiu <claudiu.beznea@...on.dev>
Cc: wim@...ux-watchdog.org, 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, Apr 10, 2024 at 04:40:43PM +0300, Claudiu 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.
> 
> 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>

Reviewed-by: Guenter Roeck <linux@...ck-us.net>

> ---
> 
> 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
>