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

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Date:   Fri, 1 Dec 2017 15:34:04 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Lukas Wunner <lukas@...ner.de>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        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 1, 2017 at 3:18 PM, Lukas Wunner <lukas@...ner.de> wrote:
> 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?

Right.

Thanks,
Rafael