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Message-ID: <CAH5fLgg6OnKLPiXXF9skpq4g7jVqgw5rJjJsLschYX5E072m2Q@mail.gmail.com>
Date: Fri, 6 Dec 2024 16:23:54 +0100
From: Alice Ryhl <aliceryhl@...gle.com>
To: Lyude Paul <lyude@...hat.com>
Cc: dri-devel@...ts.freedesktop.org, rust-for-linux@...r.kernel.org,
Asahi Lina <lina@...hilina.net>, Danilo Krummrich <dakr@...nel.org>, mcanal@...lia.com,
airlied@...hat.com, zhiw@...dia.com, cjia@...dia.com, jhubbard@...dia.com,
Miguel Ojeda <ojeda@...nel.org>, Alex Gaynor <alex.gaynor@...il.com>,
Wedson Almeida Filho <wedsonaf@...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@...sung.com>,
Trevor Gross <tmgross@...ch.edu>, Danilo Krummrich <dakr@...hat.com>,
Mika Westerberg <mika.westerberg@...ux.intel.com>, open list <linux-kernel@...r.kernel.org>
Subject: Re: [WIP RFC v2 02/35] WIP: rust: drm: Add traits for registering KMS devices
On Tue, Oct 1, 2024 at 1:37 AM Lyude Paul <lyude@...hat.com> wrote:
>
> This commit adds some traits for registering DRM devices with KMS support,
> implemented through the kernel::drm::kms::Kms trait. Devices which don't
> have KMS support can simply use PhantomData<Self>.
>
> Signed-off-by: Lyude Paul <lyude@...hat.com>
>
> ---
>
> TODO:
> * Generate feature flags automatically, these shouldn't need to be
> specified by the user
>
> Signed-off-by: Lyude Paul <lyude@...hat.com>
> ---
> rust/bindings/bindings_helper.h | 4 +
> rust/kernel/drm/device.rs | 18 ++-
> rust/kernel/drm/drv.rs | 45 ++++++-
> rust/kernel/drm/kms.rs | 230 ++++++++++++++++++++++++++++++++
> rust/kernel/drm/kms/fbdev.rs | 45 +++++++
> rust/kernel/drm/mod.rs | 1 +
> 6 files changed, 335 insertions(+), 8 deletions(-)
> create mode 100644 rust/kernel/drm/kms.rs
> create mode 100644 rust/kernel/drm/kms/fbdev.rs
>
> diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h
> index 04898f70ef1b8..4a8e44e11c96a 100644
> --- a/rust/bindings/bindings_helper.h
> +++ b/rust/bindings/bindings_helper.h
> @@ -6,11 +6,15 @@
> * Sorted alphabetically.
> */
>
> +#include <drm/drm_atomic.h>
> +#include <drm/drm_atomic_helper.h>
> #include <drm/drm_device.h>
> #include <drm/drm_drv.h>
> #include <drm/drm_file.h>
> #include <drm/drm_fourcc.h>
> +#include <drm/drm_fbdev_dma.h>
> #include <drm/drm_gem.h>
> +#include <drm/drm_gem_framebuffer_helper.h>
> #include <drm/drm_gem_shmem_helper.h>
> #include <drm/drm_ioctl.h>
> #include <kunit/test.h>
> diff --git a/rust/kernel/drm/device.rs b/rust/kernel/drm/device.rs
> index 2b687033caa2d..d4d6b1185f6a6 100644
> --- a/rust/kernel/drm/device.rs
> +++ b/rust/kernel/drm/device.rs
> @@ -5,14 +5,22 @@
> //! C header: [`include/linux/drm/drm_device.h`](srctree/include/linux/drm/drm_device.h)
>
> use crate::{
> - bindings, device, drm,
> - drm::drv::AllocImpl,
> + bindings, device,
> + drm::{
> + drv::AllocImpl,
> + self,
> + kms::{KmsImpl, private::KmsImpl as KmsImplPrivate}
> + },
> error::code::*,
> error::from_err_ptr,
> error::Result,
> types::{ARef, AlwaysRefCounted, ForeignOwnable, Opaque},
> };
> -use core::{ffi::c_void, marker::PhantomData, ptr::NonNull};
> +use core::{
> + ffi::c_void,
> + marker::PhantomData,
> + ptr::NonNull
> +};
>
> #[cfg(CONFIG_DRM_LEGACY)]
> macro_rules! drm_legacy_fields {
> @@ -150,6 +158,10 @@ pub fn data(&self) -> <T::Data as ForeignOwnable>::Borrowed<'_> {
> // SAFETY: `Self::data` is always converted and set on device creation.
> unsafe { <T::Data as ForeignOwnable>::from_foreign(drm.raw_data()) };
> }
> +
> + pub(crate) const fn has_kms() -> bool {
> + <T::Kms as KmsImplPrivate>::MODE_CONFIG_OPS.is_some()
> + }
> }
>
> // SAFETY: DRM device objects are always reference counted and the get/put functions
> diff --git a/rust/kernel/drm/drv.rs b/rust/kernel/drm/drv.rs
> index 0cf3fb1cea53c..6b61f2755ba79 100644
> --- a/rust/kernel/drm/drv.rs
> +++ b/rust/kernel/drm/drv.rs
> @@ -8,7 +8,15 @@
> alloc::flags::*,
> bindings,
> devres::Devres,
> - drm,
> + drm::{
> + self,
> + kms::{
> + KmsImpl,
> + private::KmsImpl as KmsImplPrivate,
> + Kms
> + }
> + },
> + device,
> error::{Error, Result},
> private::Sealed,
> str::CStr,
> @@ -142,6 +150,12 @@ pub trait Driver {
> /// The type used to represent a DRM File (client)
> type File: drm::file::DriverFile;
>
> + /// The KMS implementation for this driver.
> + ///
> + /// Drivers that wish to support KMS should pass their implementation of `drm::kms::KmsDriver`
> + /// here. Drivers which do not have KMS support can simply pass `drm::kms::NoKms` here.
> + type Kms: drm::kms::KmsImpl<Driver = Self> where Self: Sized;
Associated types are not really intended for optional behavior. Can't
you move this to a separate trait instead of using an associated type?
> /// Driver metadata
> const INFO: DriverInfo;
>
> @@ -159,21 +173,36 @@ pub trait Driver {
>
> impl<T: Driver> Registration<T> {
> /// Creates a new [`Registration`] and registers it.
> - pub fn new(drm: ARef<drm::device::Device<T>>, flags: usize) -> Result<Self> {
> + pub fn new(dev: &device::Device, data: T::Data, flags: usize) -> Result<Self> {
> + let drm = drm::device::Device::<T>::new(dev, data)?;
> + let has_kms = drm::device::Device::<T>::has_kms();
> +
> + let mode_config_info = if has_kms {
> + // SAFETY: We have yet to register this device
> + Some(unsafe { T::Kms::setup_kms(&drm)? })
> + } else {
> + None
> + };
> +
> // SAFETY: Safe by the invariants of `drm::device::Device`.
> let ret = unsafe { bindings::drm_dev_register(drm.as_raw(), flags as u64) };
> if ret < 0 {
> return Err(Error::from_errno(ret));
> }
>
> + if let Some(ref info) = mode_config_info {
> + // SAFETY: We just registered the device above
> + unsafe { T::Kms::setup_fbdev(&drm, info) };
> + }
> +
> Ok(Self(drm))
> }
>
> /// Same as [`Registration::new`}, but transfers ownership of the [`Registration`] to `Devres`.
> - pub fn new_foreign_owned(drm: ARef<drm::device::Device<T>>, flags: usize) -> Result {
> - let reg = Registration::<T>::new(drm.clone(), flags)?;
> + pub fn new_foreign_owned(dev: &device::Device, data: T::Data, flags: usize) -> Result {
> + let reg = Registration::<T>::new(dev, data, flags)?;
>
> - Devres::new_foreign_owned(drm.as_ref(), reg, GFP_KERNEL)
> + Devres::new_foreign_owned(dev, reg, GFP_KERNEL)
> }
>
> /// Returns a reference to the `Device` instance for this registration.
> @@ -195,5 +224,11 @@ fn drop(&mut self) {
> // SAFETY: Safe by the invariant of `ARef<drm::device::Device<T>>`. The existance of this
> // `Registration` also guarantees the this `drm::device::Device` is actually registered.
> unsafe { bindings::drm_dev_unregister(self.0.as_raw()) };
> +
> + if drm::device::Device::<T>::has_kms() {
> + // SAFETY: We just checked above that KMS was setup for this device, so this is safe to
> + // call
> + unsafe { bindings::drm_atomic_helper_shutdown(self.0.as_raw()) }
> + }
> }
> }
> diff --git a/rust/kernel/drm/kms.rs b/rust/kernel/drm/kms.rs
> new file mode 100644
> index 0000000000000..d3558a5eccc54
> --- /dev/null
> +++ b/rust/kernel/drm/kms.rs
> @@ -0,0 +1,230 @@
> +// SPDX-License-Identifier: GPL-2.0 OR MIT
> +
> +//! KMS driver abstractions for rust.
> +
> +pub mod fbdev;
> +
> +use crate::{
> + drm::{
> + drv::Driver,
> + device::Device
> + },
> + device,
> + prelude::*,
> + types::*,
> + error::to_result,
> + private::Sealed,
> +};
> +use core::{
> + ops::Deref,
> + ptr::{self, NonNull},
> + mem::{self, ManuallyDrop},
> + marker::PhantomData,
> +};
> +use bindings;
> +
> +/// The C vtable for a [`Device`].
> +///
> +/// This is created internally by DRM.
> +pub(crate) struct ModeConfigOps {
> + pub(crate) kms_vtable: bindings::drm_mode_config_funcs,
> + pub(crate) kms_helper_vtable: bindings::drm_mode_config_helper_funcs
> +}
> +
> +/// A trait representing a type that can be used for setting up KMS, or a stub.
> +///
> +/// For drivers which don't have KMS support, the methods provided by this trait may be stubs. It is
> +/// implemented internally by DRM.
> +pub trait KmsImpl: private::KmsImpl {}
> +
> +pub(crate) mod private {
> + use super::*;
> +
> + /// Private callback implemented internally by DRM for setting up KMS on a device, or stubbing
> + /// the KMS setup for devices which don't have KMS support can just use [`PhantomData`].
> + pub trait KmsImpl {
I noticed you use sealing a lot. Why?
> + /// The parent driver for this KMS implementation
> + type Driver: Driver;
> +
> + /// The optional KMS callback operations for this driver.
> + const MODE_CONFIG_OPS: Option<ModeConfigOps>;
> +
> + /// The callback for setting up KMS on a device
> + ///
> + /// # Safety
> + ///
> + /// `drm` must be unregistered.
> + unsafe fn setup_kms(drm: &Device<Self::Driver>) -> Result<ModeConfigInfo> {
> + build_error::build_error("This should never be reachable")
This pattern makes sense for #[vtable] users, but I don't think it
makes sense here. You always override these methods, so you can leave
them without a body here.
> + }
> +
> + /// The callback for setting up fbdev emulation on a KMS device.
> + ///
> + /// # Safety
> + ///
> + /// `drm` must be registered.
> + unsafe fn setup_fbdev(drm: &Device<Self::Driver>, mode_config_info: &ModeConfigInfo) {
> + build_error::build_error("This should never be reachable")
> + }
> + }
> +}
> +
> +/// A [`Device`] with KMS initialized that has not been registered with userspace.
> +///
> +/// This type is identical to [`Device`], except that it is able to create new static KMS resources.
> +/// It represents a KMS device that is not yet visible to userspace, and also contains miscellaneous
> +/// state required during the initialization process of a [`Device`].
> +pub struct UnregisteredKmsDevice<'a, T: Driver> {
> + drm: &'a Device<T>,
> +}
> +
> +impl<'a, T: Driver> Deref for UnregisteredKmsDevice<'a, T> {
> + type Target = Device<T>;
> +
> + fn deref(&self) -> &Self::Target {
> + self.drm
> + }
> +}
> +
> +impl<'a, T: Driver> UnregisteredKmsDevice<'a, T> {
> + /// Construct a new [`UnregisteredKmsDevice`].
> + ///
> + /// # Safety
> + ///
> + /// The caller promises that `drm` is an unregistered [`Device`].
> + pub(crate) unsafe fn new(drm: &'a Device<T>) -> Self {
> + Self {
> + drm,
> + }
> + }
> +}
> +
> +/// A trait which must be implemented by drivers that wish to support KMS
> +///
> +/// It should be implemented for the same type that implements [`Driver`]. Drivers which don't
> +/// support KMS should use [`PhantomData<Self>`].
> +///
> +/// [`PhantomData<Self>`]: PhantomData
> +#[vtable]
> +pub trait Kms {
> + /// The parent [`Driver`] for this [`Device`].
> + type Driver: KmsDriver;
> +
> + /// The fbdev implementation to use for this [`Device`].
> + ///
> + /// Which implementation may be used here depends on the GEM implementation specified in
> + /// [`Driver::Object`]. See [`fbdev`] for more information.
> + type Fbdev: fbdev::FbdevImpl;
> +
> + /// Return a [`ModeConfigInfo`] structure for this [`device::Device`].
> + fn mode_config_info(
> + dev: &device::Device,
> + drm_data: <<Self::Driver as Driver>::Data as ForeignOwnable>::Borrowed<'_>,
> + ) -> Result<ModeConfigInfo>;
> +
> + /// Create mode objects like [`crtc::Crtc`], [`plane::Plane`], etc. for this device
> + fn create_objects(drm: &UnregisteredKmsDevice<'_, Self::Driver>) -> Result;
> +}
> +
> +impl<T: Kms> private::KmsImpl for T {
> + type Driver = T::Driver;
> +
> + const MODE_CONFIG_OPS: Option<ModeConfigOps> = Some(ModeConfigOps {
> + kms_vtable: bindings::drm_mode_config_funcs {
> + atomic_check: Some(bindings::drm_atomic_helper_check),
> + // TODO TODO: There are other possibilities then this function, but we need
> + // to write up more bindings before we can support those
> + fb_create: Some(bindings::drm_gem_fb_create),
> + mode_valid: None, // TODO
> + atomic_commit: Some(bindings::drm_atomic_helper_commit),
> + get_format_info: None,
> + atomic_state_free: None,
> + atomic_state_alloc: None,
> + atomic_state_clear: None,
> + output_poll_changed: None,
> + },
> +
> + kms_helper_vtable: bindings::drm_mode_config_helper_funcs {
> + atomic_commit_setup: None, // TODO
> + atomic_commit_tail: None, // TODO
> + },
> + });
> +
> + unsafe fn setup_kms(drm: &Device<Self::Driver>) -> Result<ModeConfigInfo> {
> + let mode_config_info = T::mode_config_info(drm.as_ref(), drm.data())?;
> +
> + // SAFETY: `MODE_CONFIG_OPS` is always Some() in this implementation
> + let ops = unsafe { T::MODE_CONFIG_OPS.as_ref().unwrap_unchecked() };
> +
> + // SAFETY:
> + // - This function can only be called before registration via our safety contract.
> + // - Before registration, we are the only ones with access to this device.
> + unsafe {
> + (*drm.as_raw()).mode_config = bindings::drm_mode_config {
> + funcs: &ops.kms_vtable,
> + helper_private: &ops.kms_helper_vtable,
> + min_width: mode_config_info.min_resolution.0,
> + min_height: mode_config_info.min_resolution.1,
> + max_width: mode_config_info.max_resolution.0,
> + max_height: mode_config_info.max_resolution.1,
> + cursor_width: mode_config_info.max_cursor.0,
> + cursor_height: mode_config_info.max_cursor.1,
> + preferred_depth: mode_config_info.preferred_depth,
> + ..Default::default()
> + };
> + }
> +
> + // SAFETY: We just setup all of the required info this function needs in `drm_device`
> + to_result(unsafe { bindings::drmm_mode_config_init(drm.as_raw()) })?;
> +
> + // SAFETY: `drm` is guaranteed to be unregistered via our safety contract.
> + let drm = unsafe { UnregisteredKmsDevice::new(drm) };
> +
> + T::create_objects(&drm)?;
> +
> + // TODO: Eventually add a hook to customize how state readback happens, for now just reset
> + // SAFETY: Since all static modesetting objects were created in `T::create_objects()`, and
> + // that is the only place they can be created, this fulfills the C API requirements.
> + unsafe { bindings::drm_mode_config_reset(drm.as_raw()) };
> +
> + Ok(mode_config_info)
> + }
> +
> + unsafe fn setup_fbdev(drm: &Device<Self::Driver>, mode_config_info: &ModeConfigInfo) {
> + <<T as Kms>::Fbdev as fbdev::private::FbdevImpl>::setup_fbdev(drm, mode_config_info)
> + }
> +}
> +
> +impl<T: Kms> KmsImpl for T {}
> +
> +impl<T: Driver> private::KmsImpl for PhantomData<T> {
> + type Driver = T;
> +
> + const MODE_CONFIG_OPS: Option<ModeConfigOps> = None;
> +}
> +
> +impl<T: Driver> KmsImpl for PhantomData<T> {}
> +
> +/// Various device-wide information for a [`Device`] that is provided during initialization.
> +#[derive(Copy, Clone)]
> +pub struct ModeConfigInfo {
> + /// The minimum (w, h) resolution this driver can support
> + pub min_resolution: (i32, i32),
> + /// The maximum (w, h) resolution this driver can support
> + pub max_resolution: (i32, i32),
> + /// The maximum (w, h) cursor size this driver can support
> + pub max_cursor: (u32, u32),
> + /// The preferred depth for dumb ioctls
> + pub preferred_depth: u32,
> +}
> +
> +/// A [`Driver`] with [`Kms`] implemented.
> +///
> +/// This is implemented internally by DRM for any [`Device`] whose [`Driver`] type implements
> +/// [`Kms`], and provides access to methods which are only safe to use with KMS devices.
> +pub trait KmsDriver: Driver {}
> +
> +impl<T, K> KmsDriver for T
> +where
> + T: Driver<Kms = K>,
> + K: Kms<Driver = T> {}
> diff --git a/rust/kernel/drm/kms/fbdev.rs b/rust/kernel/drm/kms/fbdev.rs
> new file mode 100644
> index 0000000000000..bdf97500137d8
> --- /dev/null
> +++ b/rust/kernel/drm/kms/fbdev.rs
> @@ -0,0 +1,45 @@
> +//! Fbdev helper implementations for rust.
> +//!
> +//! This module provides the various Fbdev implementations that can be used by Rust KMS drivers.
> +use core::marker::*;
> +use crate::{private::Sealed, drm::{kms::*, device::Device, gem}};
> +use bindings;
> +
> +pub(crate) mod private {
> + use super::*;
> +
> + pub trait FbdevImpl {
> + /// Setup the fbdev implementation for this KMS driver.
> + fn setup_fbdev<T: Driver>(drm: &Device<T>, mode_config_info: &ModeConfigInfo);
> + }
> +}
> +
> +/// The main trait for a driver's DRM implementation.
> +///
> +/// Drivers are expected not to implement this directly, and to instead use one of the objects
> +/// provided by this module such as [`FbdevDma`].
> +pub trait FbdevImpl: private::FbdevImpl {}
> +
> +/// The fbdev implementation for drivers using the gem DMA helpers.
> +///
> +/// Drivers which use the gem DMA helpers ([`gem::Object`]) should use this for their [`Kms::Fbdev`]
> +/// type.
> +pub struct FbdevDma<T: Driver>(PhantomData<T>);
> +
> +impl<T, G> private::FbdevImpl for FbdevDma<T>
> +where
> + T: Driver<Object = gem::Object<G>>,
> + G: gem::DriverObject
> +{
> + #[inline]
> + fn setup_fbdev<D: Driver>(drm: &Device<D>, mode_config_info: &ModeConfigInfo) {
> + // SAFETY: Our implementation bounds re proof that this driver is using the gem dma helpers
> + unsafe { bindings::drm_fbdev_dma_setup(drm.as_raw(), mode_config_info.preferred_depth) };
> + }
> +}
> +
> +impl<T, G> FbdevImpl for FbdevDma<T>
> +where
> + T: Driver<Object = gem::Object<G>>,
> + G: gem::DriverObject
> +{}
> diff --git a/rust/kernel/drm/mod.rs b/rust/kernel/drm/mod.rs
> index 2c12dbd181997..049ae675cb9b1 100644
> --- a/rust/kernel/drm/mod.rs
> +++ b/rust/kernel/drm/mod.rs
> @@ -8,3 +8,4 @@
> pub mod fourcc;
> pub mod gem;
> pub mod ioctl;
> +pub mod kms;
> --
> 2.46.1
>
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