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

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Message-ID: <CAMuHMdWxeKWJ8hDG=GHngJzGxs_pDe3oGeok38S_PhxQy194RA@mail.gmail.com>
Date: Thu, 22 May 2025 16:55:53 +0200
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Ulf Hansson <ulf.hansson@...aro.org>
Cc: Claudiu Beznea <claudiu.beznea@...on.dev>, Dmitry Torokhov <dmitry.torokhov@...il.com>, 
	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, 
	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

Hi Ulf,

On Thu, 22 May 2025 at 13:54, Ulf Hansson <ulf.hansson@...aro.org> wrote:
> On Thu, 22 May 2025 at 11:48, Claudiu Beznea <claudiu.beznea@...on.dev> wrote:
> > I may have missed considering things when describing the case 2 (which is
> > what is proposed by this patch) as I don't have the full picture behind the
> > dev_pm_domain_detach() call in platform bus remove. If so, please correct me.
>
> The dev_pm_domain_attach|detach() calls in bus level code
> (probe/remove) were added there a long time ago, way before devres was
> being used like today.
>
> Currently we also have devm_pm_domain_attach_list(), which is used
> when devices have multiple PM domains to attach too. This is *not*
> called by bus-level code, but by the driver themselves. For these
> cases, we would not encounter the problems you have been facing with
> clocks/IRQ-handler, I think - because the devres order is maintained
> for PM domains too.
>
> 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.

IMO that sounds like going in the wrong direction.  Why would a driver
need to care if the device it manages is not located in a PM domain,
located in a single PM domain, or located in multiple PM domains?
All of this depends on SoC integration, not on the device that's
being driven. The nice thing about doing all this in the bus level
code is that it is abstracted away for the device driver (modulo using
pm_runtime_*() calls).

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds