linux-kernel - Re: [PATCH] PM / runtime: Fix handling of suppliers with disabled runtime PM

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Message-ID: <20171201141801.GA20189@wunner.de>
Date:   Fri, 1 Dec 2017 15:18:01 +0100
From:   Lukas Wunner <lukas@...ner.de>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:     Linux PM <linux-pm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH] PM / runtime: Fix handling of suppliers with disabled
 runtime PM

On Fri, Dec 01, 2017 at 02:58:34PM +0100, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> 
> Prevent rpm_get_suppliers() from returning an error code if runtime
> PM is disabled for one or more of the supplier devices it wants to
> runtime-resume, so as to make runtime PM work for devices with links
> to suppliers that don't use runtime PM (such links may be created
> during device enumeration even before it is known whether or not
> runtime PM will be enabled for the devices in question, for example).
> 
> Reported-by: Adrian Hunter <adrian.hunter@...el.com>
> Fixes: 21d5c57b3726 (PM / runtime: Use device links)
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> ---
>  drivers/base/power/runtime.c |    3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> Index: linux-pm/drivers/base/power/runtime.c
> ===================================================================
> --- linux-pm.orig/drivers/base/power/runtime.c
> +++ linux-pm/drivers/base/power/runtime.c
> @@ -276,7 +276,8 @@ static int rpm_get_suppliers(struct devi
>  			continue;
>  
>  		retval = pm_runtime_get_sync(link->supplier);
> -		if (retval < 0) {
> +		/* Ignore suppliers with disabled runtime PM. */
> +		if (retval < 0 && retval != -EACCES) {
>  			pm_runtime_put_noidle(link->supplier);
>  			return retval;
>  		}
> 

You could alternatively call pm_runtime_get_sync() under the condition
link->supplier->power.disable_depth > 0 but then the usage_count wouldn't
be incremented and I guess we want that in case runtime PM is only
temporarily disabled and later enabled, right?

I'm wondering if checking for that condition in lieu of retval != -EACCES
would be more explicit and less fragile here (there's a theoretical
possibility that the supplier's ->runtime_resume callback returns -EACCESS,
leading to a false positive).

Apart from that,

Reviewed-by: Lukas Wunner <lukas@...ner.de>

Thanks,

Lukas