linux-kernel - Re: [PATCH v3 2/4] rust: driver: Add ACPI id table support to Adapter trait

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Message-ID: <aEVqgUtflBCzZi1X@pollux>
Date: Sun, 8 Jun 2025 12:48:33 +0200
From: Danilo Krummrich <dakr@...nel.org>
To: Benno Lossin <lossin@...nel.org>
Cc: Igor Korotin <igor.korotin.linux@...il.com>, ojeda@...nel.org,
	alex.gaynor@...il.com, rafael@...nel.org,
	gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
	rust-for-linux@...r.kernel.org, linux-acpi@...r.kernel.org,
	boqun.feng@...il.com, gary@...yguo.net, bjorn3_gh@...tonmail.com,
	benno.lossin@...ton.me, a.hindborg@...nel.org, aliceryhl@...gle.com,
	tmgross@...ch.edu, lenb@...nel.org, wedsonaf@...il.com,
	viresh.kumar@...aro.org, alex.hung@....com,
	dingxiangfei2009@...il.com, Igor Korotin <igorkor.3vium@...il.com>
Subject: Re: [PATCH v3 2/4] rust: driver: Add ACPI id table support to
 Adapter trait

On Sun, Jun 08, 2025 at 09:54:30AM +0200, Benno Lossin wrote:
> On Fri Jun 6, 2025 at 7:08 PM CEST, Igor Korotin wrote:
> > @@ -141,6 +141,38 @@ pub trait Adapter {
> >      /// The type holding driver private data about each device id supported by the driver.
> >      type IdInfo: 'static;
> >  
> > +    /// The [`acpi::IdTable`] of the corresponding driver
> > +    fn acpi_id_table() -> Option<acpi::IdTable<Self::IdInfo>>;
> > +
> > +    /// Returns the driver's private data from the matching entry in the [`acpi::IdTable`], if any.
> > +    ///
> > +    /// If this returns `None`, it means there is no match with an entry in the [`acpi::IdTable`].
> > +    #[cfg(CONFIG_ACPI)]
> > +    fn acpi_id_info(dev: &device::Device) -> Option<&'static Self::IdInfo> {
> > +        let table = Self::acpi_id_table()?;
> > +
> > +        // SAFETY:
> > +        // - `table` has static lifetime, hence it's valid for read,
> > +        // - `dev` is guaranteed to be valid while it's alive, and so is `pdev.as_ref().as_raw()`.
> > +        let raw_id = unsafe { bindings::acpi_match_device(table.as_ptr(), dev.as_raw()) };
> > +
> > +        if raw_id.is_null() {
> > +            None
> > +        } else {
> > +            // SAFETY: `DeviceId` is a `#[repr(transparent)` wrapper of `struct of_device_id` and
> > +            // does not add additional invariants, so it's safe to transmute.
> > +            let id = unsafe { &*raw_id.cast::<acpi::DeviceId>() };
> > +
> > +            Some(table.info(<acpi::DeviceId as crate::device_id::RawDeviceId>::index(id)))
> > +        }
> > +    }
> > +
> > +    #[cfg(not(CONFIG_ACPI))]
> > +    #[allow(missing_docs)]
> 
> I think we should change this to one single definition and do
> 
>     if cfg!(not(CONFIG_ACPI)) {
>         return None;
>     }
>     /* body from above */
> 
> In a single function instead.

Generally, that's fine, but in this case I'd rather keep it as it is for
consistency with the rest of the file.

> > +    fn acpi_id_info(_dev: &device::Device) -> Option<&'static Self::IdInfo> {
> > +        None
> > +    }
> > +
> >      /// The [`of::IdTable`] of the corresponding driver.
> >      fn of_id_table() -> Option<of::IdTable<Self::IdInfo>>;
> >  
> > @@ -178,6 +210,11 @@ fn of_id_info(_dev: &device::Device) -> Option<&'static Self::IdInfo> {
> >      /// If this returns `None`, it means that there is no match in any of the ID tables directly
> >      /// associated with a [`device::Device`].
> >      fn id_info(dev: &device::Device) -> Option<&'static Self::IdInfo> {
> > +        let id = Self::acpi_id_info(dev);
> > +        if id.is_some() {
> > +            return id;
> > +        }
> 
> Is a driver only going to have one id_info? Or is there some kind of
> precedence?

A driver potentially has lots of them, but the device is only matching a single
entry in one of the driver's ID tables and hence a single ID info.