linux-kernel - Re: [PATCH RFC 02/18] rust: drm: Add Device and Driver abstractions

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Message-ID: <ZAwUbAWvPt9aavXp@Boquns-Mac-mini.local>
Date:   Fri, 10 Mar 2023 21:41:00 -0800
From:   Boqun Feng <boqun.feng@...il.com>
To:     Asahi Lina <lina@...hilina.net>
Cc:     Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Miguel Ojeda <ojeda@...nel.org>,
        Alex Gaynor <alex.gaynor@...il.com>,
        Wedson Almeida Filho <wedsonaf@...il.com>,
        Gary Guo <gary@...yguo.net>,
        Björn Roy Baron <bjorn3_gh@...tonmail.com>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Christian König <christian.koenig@....com>,
        Luben Tuikov <luben.tuikov@....com>,
        Jarkko Sakkinen <jarkko@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Alyssa Rosenzweig <alyssa@...enzweig.io>,
        Karol Herbst <kherbst@...hat.com>,
        Ella Stanforth <ella@...unix.org>,
        Faith Ekstrand <faith.ekstrand@...labora.com>,
        Mary <mary@...y.zone>, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, rust-for-linux@...r.kernel.org,
        linux-media@...r.kernel.org, linaro-mm-sig@...ts.linaro.org,
        linux-sgx@...r.kernel.org, asahi@...ts.linux.dev
Subject: Re: [PATCH RFC 02/18] rust: drm: Add Device and Driver abstractions

On Tue, Mar 07, 2023 at 11:25:27PM +0900, Asahi Lina wrote:
> Add the initial abstractions for DRM drivers and devices. These go
> together in one commit since they are fairly tightly coupled types.
> 
> A few things have been stubbed out, to be implemented as further bits of
> the DRM subsystem are introduced.
> 
> Signed-off-by: Asahi Lina <lina@...hilina.net>
> ---
>  rust/bindings/bindings_helper.h |   3 +
>  rust/kernel/drm/device.rs       |  76 +++++++++
>  rust/kernel/drm/drv.rs          | 339 ++++++++++++++++++++++++++++++++++++++++
>  rust/kernel/drm/mod.rs          |   2 +
>  4 files changed, 420 insertions(+)
> 
> diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h
> index 2687bef1676f..2a999138c4ae 100644
> --- a/rust/bindings/bindings_helper.h
> +++ b/rust/bindings/bindings_helper.h
> @@ -6,10 +6,13 @@
>   * Sorted alphabetically.
>   */
>  
> +#include <drm/drm_device.h>
> +#include <drm/drm_drv.h>
>  #include <drm/drm_ioctl.h>
>  #include <linux/delay.h>
>  #include <linux/device.h>
>  #include <linux/dma-mapping.h>
> +#include <linux/fs.h>
>  #include <linux/ioctl.h>
>  #include <linux/io-pgtable.h>
>  #include <linux/ktime.h>
> diff --git a/rust/kernel/drm/device.rs b/rust/kernel/drm/device.rs
> new file mode 100644
> index 000000000000..6007f941137a
> --- /dev/null
> +++ b/rust/kernel/drm/device.rs
> @@ -0,0 +1,76 @@
> +// SPDX-License-Identifier: GPL-2.0 OR MIT
> +
> +//! DRM device.
> +//!
> +//! C header: [`include/linux/drm/drm_device.h`](../../../../include/linux/drm/drm_device.h)
> +
> +use crate::{bindings, device, drm, types::ForeignOwnable};
> +use core::marker::PhantomData;
> +
> +/// Represents a reference to a DRM device. The device is reference-counted and is guaranteed to
> +/// not be dropped while this object is alive.
> +pub struct Device<T: drm::drv::Driver> {
> +    // Type invariant: ptr must be a valid and initialized drm_device,
> +    // and this value must either own a reference to it or the caller
> +    // must ensure that it is never dropped if the reference is borrowed.
> +    pub(super) ptr: *mut bindings::drm_device,
> +    _p: PhantomData<T>,
> +}
> +
> +impl<T: drm::drv::Driver> Device<T> {
> +    // Not intended to be called externally, except via declare_drm_ioctls!()
> +    #[doc(hidden)]
> +    pub unsafe fn from_raw(raw: *mut bindings::drm_device) -> Device<T> {
> +        Device {
> +            ptr: raw,
> +            _p: PhantomData,
> +        }
> +    }
> +
> +    #[allow(dead_code)]
> +    pub(crate) fn raw(&self) -> *const bindings::drm_device {
> +        self.ptr
> +    }
> +
> +    pub(crate) fn raw_mut(&mut self) -> *mut bindings::drm_device {
> +        self.ptr
> +    }

Since you can always get a *mut bindings::drm_device safely from

	a.raw() as *mut _

, this mutable version seems unnecesarry to me. In other words, no way
to prevent getting a *mut bindings::drm_device from only &Device.

Regards,
Boqun

> +
> +    /// Returns a borrowed reference to the user data associated with this Device.
> +    pub fn data(&self) -> <T::Data as ForeignOwnable>::Borrowed<'_> {
> +        unsafe { T::Data::borrow((*self.ptr).dev_private) }
> +    }
> +}
> +
[...]