linux-kernel - Re: [PATCH] driver core: platform: Use devres group to free driver probe resources

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Message-ID: <CAPDyKFoxs6wDCLp5EGHVqkqSstBLNmngps2KfanRezV_EN8tuA@mail.gmail.com>
Date: Fri, 23 May 2025 00:09:08 +0200
From: Ulf Hansson <ulf.hansson@...aro.org>
To: Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc: Claudiu Beznea <claudiu.beznea@...on.dev>, Jonathan Cameron <jic23@...nel.org>, 
	"Rafael J. Wysocki" <rafael@...nel.org>, Daniel Lezcano <daniel.lezcano@...aro.org>, dakr@...nel.org, 
	linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org, 
	linux-renesas-soc@...r.kernel.org, geert@...ux-m68k.org, 
	Claudiu Beznea <claudiu.beznea.uj@...renesas.com>, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, linux-iio@...r.kernel.org, bhelgaas@...gle.com
Subject: Re: [PATCH] driver core: platform: Use devres group to free driver
 probe resources

On Thu, 22 May 2025 at 20:47, Dmitry Torokhov <dmitry.torokhov@...il.com> wrote:
>
> On Thu, May 22, 2025 at 06:28:44PM +0200, Ulf Hansson wrote:
> > On Thu, 22 May 2025 at 16:08, Claudiu Beznea <claudiu.beznea@...on.dev> wrote:
> > >
> > > Hi, Ulf,
> > >
> > > On 22.05.2025 14:53, Ulf Hansson wrote:
> > > >
> > > > That said, I think adding a devm_pm_domain_attach() interface would
> > > > make perfect sense. Then we can try to replace
> > > > dev_pm_domain_attach|detach() in bus level code, with just a call to
> > > > devm_pm_domain_attach(). In this way, we should preserve the
> > > > expectation for drivers around devres for PM domains. Even if it would
> > > > change the behaviour for some drivers, it still sounds like the
> > > > correct thing to do in my opinion.
> > >
> > > This looks good to me, as well. I did prototype it on my side and tested on
> > > all my failure cases and it works.
> >
> > That's great! I am happy to help review, if/when you decide to post it.
>
> So you are saying you'd be OK with essentially the following (with
> devm_pm_domain_attach() actually being elsewhere in a real patch and not
> necessarily mimicked by devm_add_action_or_reset()):

Correct!

>
> diff --git a/drivers/base/platform.c b/drivers/base/platform.c
> index cfccf3ff36e7..1e017bfa5caf 100644
> --- a/drivers/base/platform.c
> +++ b/drivers/base/platform.c
> @@ -1376,6 +1376,27 @@ static int platform_uevent(const struct device *dev, struct kobj_uevent_env *env
>         return 0;
>  }
>
> +
> +static void platform_pm_domain_detach(void *d)
> +{
> +       dev_pm_domain_detach(d, true);
> +}

Well, I would not limit this to the platform bus, even if that is the
most widely used.

Let's add the new generic interface along with
dev_pm_domain_attach|detach* and friends instead.

Then we can convert bus level code (and others), such as the platform
bus to use it, in a step-by-step approach.

> +
> +static int devm_pm_domain_attach(struct device *dev)
> +{
> +       int error;
> +
> +       error = dev_pm_domain_attach(dev, true);
> +       if (error)
> +               return error;
> +
> +       error = devm_add_action_or_reset(dev, platform_pm_domain_detach, dev);
> +       if (error)
> +               return error;
> +
> +       return 0;
> +}
> +
>  static int platform_probe(struct device *_dev)
>  {
>         struct platform_driver *drv = to_platform_driver(_dev->driver);
> @@ -1396,15 +1417,12 @@ static int platform_probe(struct device *_dev)
>         if (ret < 0)
>                 return ret;
>
> -       ret = dev_pm_domain_attach(_dev, true);
> +       ret = devm_pm_domain_attach(_dev);
>         if (ret)
>                 goto out;
>
> -       if (drv->probe) {
> +       if (drv->probe)
>                 ret = drv->probe(dev);
> -               if (ret)
> -                       dev_pm_domain_detach(_dev, true);
> -       }
>
>  out:
>         if (drv->prevent_deferred_probe && ret == -EPROBE_DEFER) {
> @@ -1422,7 +1440,6 @@ static void platform_remove(struct device *_dev)
>
>         if (drv->remove)
>                 drv->remove(dev);
> -       dev_pm_domain_detach(_dev, true);
>  }
>
>  static void platform_shutdown(struct device *_dev)
>
>
> If so, then OK, it will work for me as well. This achieves the
> same behavior as with using devres group. The only difference is that if
> we ever need to extend the platform bus to acquire/release more
> resources they will also have to use devm API and not the regular one.

Sounds reasonable to me! Thanks for a nice discussion!

When it comes to the devm_pm_runtime_enable() API, I think we
seriously should consider removing it. Let me have a closer look at
that.

Kind regards
Uffe