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

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Message-Id: <DAH4KX3Y3M3P.3B82LSVWU172Q@kernel.org>
Date: Sun, 08 Jun 2025 13:46:17 +0200
From: "Benno Lossin" <lossin@...nel.org>
To: "Danilo Krummrich" <dakr@...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 8, 2025 at 12:48 PM CEST, Danilo Krummrich wrote:
> 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.

Then let's also change the OF bindings in this file to that style :)

>> > +    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.

Ah so if `of_id_info` and `acpi_id_info` return `Some(_)`, then both
values are the same?

---
Cheers,
Benno