Message-ID: <4360ee7a-d85a-4fa0-a1d6-d09a3b9d57c0@tuxon.dev>
Date: Mon, 16 Jun 2025 12:37:41 +0300
From: Claudiu Beznea <claudiu.beznea@...on.dev>
To: "Rafael J. Wysocki" <rafael@...nel.org>
Cc: Jonathan Cameron <jic23@...nel.org>,
 Dmitry Torokhov <dmitry.torokhov@...il.com>, gregkh@...uxfoundation.org,
 dakr@...nel.org, len.brown@...el.com, pavel@...nel.org,
 ulf.hansson@...aro.org, daniel.lezcano@...aro.org,
 linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org, bhelgaas@...gle.com,
 geert@...ux-m68k.org, linux-iio@...r.kernel.org,
 linux-renesas-soc@...r.kernel.org, fabrizio.castro.jz@...esas.com,
 Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
Subject: Re: [PATCH v3 1/2] PM: domains: Add devres variant for
 dev_pm_domain_attach()

Hi, Rafael,

On 13.06.2025 13:02, Rafael J. Wysocki wrote:
> On Fri, Jun 13, 2025 at 9:39 AM Claudiu Beznea <claudiu.beznea@...on.dev> wrote:
>>
>> Hi, Rafael,
>>
>> On 09.06.2025 22:59, Rafael J. Wysocki wrote:
>>> On Sat, Jun 7, 2025 at 3:06 PM Jonathan Cameron <jic23@...nel.org> wrote:
>>>>
>>>> On Fri, 6 Jun 2025 22:01:52 +0200
>>>> "Rafael J. Wysocki" <rafael@...nel.org> wrote:
>>>>
>>>> Hi Rafael,
>>>>
>>>>> On Fri, Jun 6, 2025 at 8:55 PM Dmitry Torokhov
>>>>> <dmitry.torokhov@...il.com> wrote:
>>>>>>
>>>>>> On Fri, Jun 06, 2025 at 06:00:34PM +0200, Rafael J. Wysocki wrote:
>>>>>>> On Fri, Jun 6, 2025 at 1:18 PM Claudiu <claudiu.beznea@...on.dev> wrote:
>>>>>>>>
>>>>>>>> From: Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
>>>>>>>>
>>>>>>>> The dev_pm_domain_attach() function is typically used in bus code alongside
>>>>>>>> dev_pm_domain_detach(), often following patterns like:
>>>>>>>>
>>>>>>>> static int bus_probe(struct device *_dev)
>>>>>>>> {
>>>>>>>>     struct bus_driver *drv = to_bus_driver(dev->driver);
>>>>>>>>     struct bus_device *dev = to_bus_device(_dev);
>>>>>>>>     int ret;
>>>>>>>>
>>>>>>>>     // ...
>>>>>>>>
>>>>>>>>     ret = dev_pm_domain_attach(_dev, true);
>>>>>>>>     if (ret)
>>>>>>>>         return ret;
>>>>>>>>
>>>>>>>>     if (drv->probe)
>>>>>>>>         ret = drv->probe(dev);
>>>>>>>>
>>>>>>>>     // ...
>>>>>>>> }
>>>>>>>>
>>>>>>>> static void bus_remove(struct device *_dev)
>>>>>>>> {
>>>>>>>>     struct bus_driver *drv = to_bus_driver(dev->driver);
>>>>>>>>     struct bus_device *dev = to_bus_device(_dev);
>>>>>>>>
>>>>>>>>     if (drv->remove)
>>>>>>>>         drv->remove(dev);
>>>>>>>>     dev_pm_domain_detach(_dev);
>>>>>>>> }
>>>>>>>>
>>>>>>>> When the driver's probe function uses devres-managed resources that depend
>>>>>>>> on the power domain state, those resources are released later during
>>>>>>>> device_unbind_cleanup().
>>>>>>>>
>>>>>>>> Releasing devres-managed resources that depend on the power domain state
>>>>>>>> after detaching the device from its PM domain can cause failures.
>>>>>>>>
>>>>>>>> For example, if the driver uses devm_pm_runtime_enable() in its probe
>>>>>>>> function, and the device's clocks are managed by the PM domain, then
>>>>>>>> during removal the runtime PM is disabled in device_unbind_cleanup() after
>>>>>>>> the clocks have been removed from the PM domain. It may happen that the
>>>>>>>> devm_pm_runtime_enable() action causes the device to be runtime-resumed.
>>>>>>>
>>>>>>> Don't use devm_pm_runtime_enable() then.
>>>>>>
>>>>>> What about other devm_ APIs? Are you suggesting that platform drivers
>>>>>> should not be using devm_clk*(), devm_regulator_*(),
>>>>>> devm_request_*_irq() and devm_add_action_or_reset()? Because again,
>>>>>> dev_pm_domain_detach() that is called by platform bus_remove() may shut
>>>>>> off the device too early, before cleanup code has a chance to execute
>>>>>> proper cleanup.
>>>>>>
>>>>>> The issue is not limited to runtime PM.
>>>>>>
>>>>>>>
>>>>>>>> If the driver specific runtime PM APIs access registers directly, this
>>>>>>>> will lead to accessing device registers without clocks being enabled.
>>>>>>>> Similar issues may occur with other devres actions that access device
>>>>>>>> registers.
>>>>>>>>
>>>>>>>> Add devm_pm_domain_attach(). When replacing the dev_pm_domain_attach() and
>>>>>>>> dev_pm_domain_detach() in bus probe and bus remove, it ensures that the
>>>>>>>> device is detached from its PM domain in device_unbind_cleanup(), only
>>>>>>>> after all driver's devres-managed resources have been release.
>>>>>>>>
>>>>>>>> For flexibility, the implemented devm_pm_domain_attach() has 2 state
>>>>>>>> arguments, one for the domain state on attach, one for the domain state on
>>>>>>>> detach.
>>>>>>>
>>>>>>> dev_pm_domain_attach() is not part driver API and I'm not convinced at
>>>>>>
>>>>>> Is the concern that devm_pm_domain_attach() will be [ab]used by drivers?
>>>>>
>>>>> Yes, among other things.
>>>>
>>>> Maybe naming could make abuse at least obvious to spot? e.g.
>>>> pm_domain_attach_with_devm_release()
>>>
>>> If I'm not mistaken, it is not even necessary to use devres for this.
>>>
>>> You might as well add a dev_pm_domain_detach() call to
>>> device_unbind_cleanup() after devres_release_all().  There is a slight
>>> complication related to the second argument of it, but I suppose that
>>> this can be determined at the attach time and stored in a new device
>>> PM flag, or similar.
>>>
>>
>> I looked into this solution. I've tested it for all my failure cases and
>> went good.
> 
> OK
> 
>>> Note that dev->pm_domain is expected to be cleared by ->detach(), so
>>> this should not cause the domain to be detached twice in a row from
>>> the same device, but that needs to be double-checked.
>>
>> The genpd_dev_pm_detach() calls genpd_remove_device() ->
>> dev_pm_domain_set(dev, NULL) which sets the dev->pm_domain = NULL. I can't
>> find any other detach function in the current code base.
> 
> There is also acpi_dev_pm_detach() which can be somewhat hard to find,
> but it calls dev_pm_domain_set(dev, NULL) either.
> 
>> The code I've tested for this solution is this one:
>>
>> diff --git a/drivers/base/dd.c b/drivers/base/dd.c
>> index b526e0e0f52d..5e9750d007b4 100644
>> --- a/drivers/base/dd.c
>> +++ b/drivers/base/dd.c
>> @@ -25,6 +25,7 @@
>>  #include <linux/kthread.h>
>>  #include <linux/wait.h>
>>  #include <linux/async.h>
>> +#include <linux/pm_domain.h>
>>  #include <linux/pm_runtime.h>
>>  #include <linux/pinctrl/devinfo.h>
>>  #include <linux/slab.h>
>> @@ -552,8 +553,11 @@ static void device_unbind_cleanup(struct device *dev)
>>         dev->dma_range_map = NULL;
>>         device_set_driver(dev, NULL);
>>         dev_set_drvdata(dev, NULL);
>> -       if (dev->pm_domain && dev->pm_domain->dismiss)
>> -               dev->pm_domain->dismiss(dev);
>> +       if (dev->pm_domain) {
>> +               if (dev->pm_domain->dismiss)
>> +                       dev->pm_domain->dismiss(dev);
>> +               dev_pm_domain_detach(dev, dev->pm_domain->detach_power_off);
> 
> I would do the "detach" before the "dismiss" to retain the current ordering.

I applied on my local development branch all your suggestions except this
one because genpd_dev_pm_detach() as well as acpi_dev_pm_detach() set
dev->pm_domain = NULL.

Due to this I would call first ->dismiss() then ->detach(), as initially
proposed. Please let me know if you consider it otherwise.

Thank you,
Claudiu

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