linux-kernel - Re: [PATCH] PM / Domains: defer dev_pm_domain_set() until genpd->attach

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Date:   Wed, 12 Jul 2017 17:36:35 +0100
From:   Sudeep Holla <sudeep.holla@....com>
To:     Ulf Hansson <ulf.hansson@...aro.org>
Cc:     Sudeep Holla <sudeep.holla@....com>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Kevin Hilman <khilman@...nel.org>
Subject: Re: [PATCH] PM / Domains: defer dev_pm_domain_set() until
 genpd->attach_dev succeeds if present



On 12/07/17 14:59, Ulf Hansson wrote:
> On 29 June 2017 at 20:00, Sudeep Holla <sudeep.holla@....com> wrote:
>> If the genpd->attach_dev or genpd->power_on fails, genpd_dev_pm_attach
>> may return -EPROBE_DEFER initially. However genpd_alloc_dev_data sets
>> the PM domain for the device unconditionally.
>>
>> When subsequent attempts are made to call genpd_dev_pm_attach, it may
>> return -EEXISTS checking dev->pm_domain without re-attempting to call
>> attach_dev or power_on.
>>
>> platform_drv_probe then attempts to call drv->probe as the return value
>> -EEXIST != -EPROBE_DEFER, which may end up in a situation where the
>> device is accessed without it's power domain switched on.
> 
> Right, this makes sense.
> 

Thanks

>>
>> Cc: "Rafael J. Wysocki" <rjw@...ysocki.net>
>> Cc: Kevin Hilman <khilman@...nel.org>
>> Cc: Ulf Hansson <ulf.hansson@...aro.org>
>> Signed-off-by: Sudeep Holla <sudeep.holla@....com>
> 
> Could we perhaps work out which commit it fixes, or perhaps the
> problem been there long time ago and we should just add a stable tag?
>

OK I will dig that out.

>> ---
>>  drivers/base/power/domain.c | 4 ++--
>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/base/power/domain.c b/drivers/base/power/domain.c
>> index da49a8383dc3..b195d34de888 100644
>> --- a/drivers/base/power/domain.c
>> +++ b/drivers/base/power/domain.c
>> @@ -1168,8 +1168,6 @@ static struct generic_pm_domain_data *genpd_alloc_dev_data(struct device *dev,
>>
>>         spin_unlock_irq(&dev->power.lock);
>>
>> -       dev_pm_domain_set(dev, &genpd->domain);
>> -
>>         return gpd_data;
>>
>>   err_free:
>> @@ -1221,6 +1219,8 @@ static int genpd_add_device(struct generic_pm_domain *genpd, struct device *dev,
>>         if (ret)
>>                 goto out;
>>
>> +       dev_pm_domain_set(dev, &genpd->domain);
>> +
>>         genpd->device_count++;
>>         genpd->max_off_time_changed = true;
>>
>> --
>> 2.7.4
>>
> 
> One piece is missing to make this fix complete.
> 
> More precisely, you must also move the call to dev_pm_domain_set(dev, NULL).
> 

Sure will add.

> Currently that is done from genpd_free_dev_data(), as it corresponds
> to genpd_alloc_dev_data(), but clearly the proper place to call it
> should be from genpd_remove_device().
> 

OK, will also look into that.

-- 
Regards,
Sudeep