linux-kernel - Re: [PATCH v2] rust: kernel: device: Add devm_of_platform

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Message-ID: <aBDl5oRIRpwbPrC1@pollux>
Date: Tue, 29 Apr 2025 16:44:54 +0200
From: Danilo Krummrich <dakr@...nel.org>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Ayush Singh <ayush@...gleboard.org>,
	Jason Kridner <jkridner@...gleboard.org>,
	Deepak Khatri <lorforlinux@...gleboard.org>,
	Robert Nelson <robertcnelson@...gleboard.org>,
	Dhruva Gole <d-gole@...com>, Miguel Ojeda <ojeda@...nel.org>,
	Alex Gaynor <alex.gaynor@...il.com>,
	Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
	Björn Roy Baron <bjorn3_gh@...tonmail.com>,
	Benno Lossin <benno.lossin@...ton.me>,
	Andreas Hindborg <a.hindborg@...nel.org>,
	Alice Ryhl <aliceryhl@...gle.com>, Trevor Gross <tmgross@...ch.edu>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] rust: kernel: device: Add
 devm_of_platform_populate/depopulate

On Tue, Apr 29, 2025 at 04:37:49PM +0200, Greg Kroah-Hartman wrote:
> On Tue, Apr 29, 2025 at 04:31:52PM +0200, Danilo Krummrich wrote:
> > On Tue, Apr 29, 2025 at 05:09:26PM +0530, Ayush Singh wrote:
> > > +    /// Remove devices populated from device tree
> > > +    pub fn devm_of_platform_depopulate(&self) {
> > > +        // SAFETY: self is valid bound Device reference
> > > +        unsafe { bindings::devm_of_platform_depopulate(self.as_raw()) }
> > > +    }
> > > +}
> > 
> > One additional question regarding devm_of_platform_depopulate(). This function
> > is only used once throughout the whole kernel (in [1]), and at a first glance
> > the usage there seems unnecessary.
> > 
> > In your upcoming driver you call devm_of_platform_depopulate() from a fallible
> > path [2].
> > 
> > So, I think we should change devm_of_platform_depopulate() to return an error
> > instead of WARN(ret).
> > 
> > If [1] needs it for some subtle reason I don't see, then I think we can still
> > call it from there as
> > 
> > 	WARN(devm_of_platform_depopulate())
> > 
> > [1] https://elixir.bootlin.com/linux/v6.15-rc4/source/drivers/soc/ti/pruss.c#L558
> > [2] https://github.com/Ayush1325/linux/commit/cdb1322b7166532445c54b601ad0a252866e574d#diff-7b9e3179e36732d5f3a681034d70c2fda4ff57745c79ad4a656f328c91e54b77R71
> 
> Ugh, no, we should just delete this function entirely if only one driver
> is using it.  That implies it's not really needed at all.

Ayush's driver calls {de}populate() from a sysfs store path [2]; not sure what
it's doing semantically or if this is a valid use-case though.