linux-kernel - Re: [PATCH] PM: Avoid false-positive warnings in dev_pm_domain

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Date:	Wed, 3 Feb 2016 10:58:21 +0100
From:	Ulf Hansson <ulf.hansson@...aro.org>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:	Linux PM list <linux-pm@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Tomeu Vizoso <tomeu.vizoso@...labora.com>,
	Kevin Hilman <khilman@...nel.org>
Subject: Re: [PATCH] PM: Avoid false-positive warnings in dev_pm_domain_set()

On 30 January 2016 at 12:54, Rafael J. Wysocki <rjw@...ysocki.net> wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
>
> There is a WARN_ON() in dev_pm_domain_set() that triggers on attempts
> to set the pm_domain pointer for devices with a driver bound.
>
> However, that WARN_ON() triggers on attempts to clear the pointer
> too and the test it uses is based on checking the device's
> p->knode_driver pointer which still is set when the device bus
> type's/driver's ->remove callback has been executed.  This
> leads to false-positive warnings when bus type code calls
> dev_pm_domain_set() to clear the pm_domain pointer after
> invoking the driver's ->remove() callback.
>
> To avoid those false-positives, make dev_pm_domain_set() check
> if the pointer passed to it is NULL and skip the warning in
> that case.
>
> Fixes: 989561de9b51 (PM / Domains: add setter for dev.pm_domain)
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> ---
>  drivers/base/power/common.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> Index: linux-pm/drivers/base/power/common.c
> ===================================================================
> --- linux-pm.orig/drivers/base/power/common.c
> +++ linux-pm/drivers/base/power/common.c
> @@ -146,7 +146,7 @@ void dev_pm_domain_set(struct device *de
>         if (dev->pm_domain == pd)
>                 return;
>
> -       WARN(device_is_bound(dev),
> +       WARN(pd && device_is_bound(dev),
>              "PM domains can only be changed for unbound devices\n");

Perhaps this information then becomes a bit misleading, as it's okay
to clear the pointer, but not assign it to a valid PM domain.

>         dev->pm_domain = pd;
>         device_pm_check_callbacks(dev);
>

Otherwise, this looks good to me!

Kind regards
Uffe