[PATCH RFC 12/18] rust: drm: sched: Add GPU scheduler abstraction

[Asahi Lina <lina@asahilina.net>]

The GPU scheduler manages scheduling GPU jobs and dependencies between
them. This Rust abstraction allows Rust DRM drivers to use this
functionality.

Signed-off-by: Asahi Lina <lina@asahilina.net>
---
 drivers/gpu/drm/Kconfig         |   5 +
 rust/bindings/bindings_helper.h |   1 +
 rust/helpers.c                  |   6 +
 rust/kernel/drm/mod.rs          |   2 +
 rust/kernel/drm/sched.rs        | 358 ++++++++++++++++++++++++++++++++++++++++
 5 files changed, 372 insertions(+)

diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
index 70a983a17ac2..8b5ad6aee126 100644
--- a/drivers/gpu/drm/Kconfig
+++ b/drivers/gpu/drm/Kconfig
@@ -39,6 +39,11 @@ config RUST_DRM_GEM_SHMEM_HELPER
 	depends on RUST_DRM
 	select DRM_GEM_SHMEM_HELPER
 
+config RUST_DRM_SCHED
+	bool
+	depends on RUST_DRM
+	select DRM_SCHED
+
 config DRM_MIPI_DBI
 	tristate
 	depends on DRM
diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h
index b6696011f3a4..dc01be08676e 100644
--- a/rust/bindings/bindings_helper.h
+++ b/rust/bindings/bindings_helper.h
@@ -13,6 +13,7 @@
 #include <drm/drm_gem_shmem_helper.h>
 #include <drm/drm_ioctl.h>
 #include <drm/drm_syncobj.h>
+#include <drm/gpu_scheduler.h>
 #include <linux/delay.h>
 #include <linux/device.h>
 #include <linux/dma-fence.h>
diff --git a/rust/helpers.c b/rust/helpers.c
index 11965b1e2f4e..1b33ed602090 100644
--- a/rust/helpers.c
+++ b/rust/helpers.c
@@ -408,6 +408,12 @@ void rust_helper___spin_lock_init(spinlock_t *lock, const char *name,
 }
 EXPORT_SYMBOL_GPL(rust_helper___spin_lock_init);
 
+unsigned long rust_helper_msecs_to_jiffies(const unsigned int m)
+{
+	return msecs_to_jiffies(m);
+}
+EXPORT_SYMBOL_GPL(rust_helper_msecs_to_jiffies);
+
 #ifdef CONFIG_DMA_SHARED_BUFFER
 
 void rust_helper_dma_fence_get(struct dma_fence *fence)
diff --git a/rust/kernel/drm/mod.rs b/rust/kernel/drm/mod.rs
index dae98826edfd..3ddf7712aab3 100644
--- a/rust/kernel/drm/mod.rs
+++ b/rust/kernel/drm/mod.rs
@@ -8,4 +8,6 @@ pub mod file;
 pub mod gem;
 pub mod ioctl;
 pub mod mm;
+#[cfg(CONFIG_RUST_DRM_SCHED)]
+pub mod sched;
 pub mod syncobj;
diff --git a/rust/kernel/drm/sched.rs b/rust/kernel/drm/sched.rs
new file mode 100644
index 000000000000..a5275cc16179
--- /dev/null
+++ b/rust/kernel/drm/sched.rs
@@ -0,0 +1,358 @@
+// SPDX-License-Identifier: GPL-2.0 OR MIT
+
+//! DRM Scheduler
+//!
+//! C header: [`include/linux/drm/gpu_scheduler.h`](../../../../include/linux/drm/gpu_scheduler.h)
+
+use crate::{
+    bindings, device,
+    dma_fence::*,
+    error::{to_result, Result},
+    prelude::*,
+    sync::{Arc, UniqueArc},
+};
+use alloc::boxed::Box;
+use core::marker::PhantomData;
+use core::mem::MaybeUninit;
+use core::ops::{Deref, DerefMut};
+use core::ptr::addr_of_mut;
+
+/// Scheduler status after timeout recovery
+#[repr(u32)]
+pub enum Status {
+    /// Device recovered from the timeout and can execute jobs again
+    Nominal = bindings::drm_gpu_sched_stat_DRM_GPU_SCHED_STAT_NOMINAL,
+    /// Device is no longer available
+    NoDevice = bindings::drm_gpu_sched_stat_DRM_GPU_SCHED_STAT_ENODEV,
+}
+
+/// Scheduler priorities
+#[repr(i32)]
+pub enum Priority {
+    /// Low userspace priority
+    Min = bindings::drm_sched_priority_DRM_SCHED_PRIORITY_MIN,
+    /// Normal userspace priority
+    Normal = bindings::drm_sched_priority_DRM_SCHED_PRIORITY_NORMAL,
+    /// High userspace priority
+    High = bindings::drm_sched_priority_DRM_SCHED_PRIORITY_HIGH,
+    /// Kernel priority (highest)
+    Kernel = bindings::drm_sched_priority_DRM_SCHED_PRIORITY_KERNEL,
+}
+
+/// Trait to be implemented by driver job objects.
+pub trait JobImpl: Sized {
+    /// Called when the scheduler is considering scheduling this job next, to get another Fence
+    /// for this job to block on. Once it returns None, run() may be called.
+    fn prepare(_job: &mut Job<Self>) -> Option<Fence> {
+        None // Equivalent to NULL function pointer
+    }
+
+    /// Called before job execution to check whether the hardware is free enough to run the job.
+    /// This can be used to implement more complex hardware resource policies than the hw_submission
+    /// limit.
+    fn can_run(_job: &mut Job<Self>) -> bool {
+        true
+    }
+
+    /// Called to execute the job once all of the dependencies have been resolved. This may be
+    /// called multiple times, if timed_out() has happened and drm_sched_job_recovery() decides
+    /// to try it again.
+    fn run(job: &mut Job<Self>) -> Result<Option<Fence>>;
+
+    /// Called when a job has taken too long to execute, to trigger GPU recovery.
+    ///
+    /// This method is called in a workqueue context.
+    fn timed_out(job: &mut Job<Self>) -> Status;
+}
+
+unsafe extern "C" fn prepare_job_cb<T: JobImpl>(
+    sched_job: *mut bindings::drm_sched_job,
+    _s_entity: *mut bindings::drm_sched_entity,
+) -> *mut bindings::dma_fence {
+    // SAFETY: All of our jobs are Job<T>.
+    let p = crate::container_of!(sched_job, Job<T>, job) as *mut Job<T>;
+
+    match T::prepare(unsafe { &mut *p }) {
+        None => core::ptr::null_mut(),
+        Some(fence) => fence.into_raw(),
+    }
+}
+
+unsafe extern "C" fn run_job_cb<T: JobImpl>(
+    sched_job: *mut bindings::drm_sched_job,
+) -> *mut bindings::dma_fence {
+    // SAFETY: All of our jobs are Job<T>.
+    let p = crate::container_of!(sched_job, Job<T>, job) as *mut Job<T>;
+
+    match T::run(unsafe { &mut *p }) {
+        Err(e) => e.to_ptr(),
+        Ok(None) => core::ptr::null_mut(),
+        Ok(Some(fence)) => fence.into_raw(),
+    }
+}
+
+unsafe extern "C" fn can_run_job_cb<T: JobImpl>(sched_job: *mut bindings::drm_sched_job) -> bool {
+    // SAFETY: All of our jobs are Job<T>.
+    let p = crate::container_of!(sched_job, Job<T>, job) as *mut Job<T>;
+
+    T::can_run(unsafe { &mut *p })
+}
+
+unsafe extern "C" fn timedout_job_cb<T: JobImpl>(
+    sched_job: *mut bindings::drm_sched_job,
+) -> bindings::drm_gpu_sched_stat {
+    // SAFETY: All of our jobs are Job<T>.
+    let p = crate::container_of!(sched_job, Job<T>, job) as *mut Job<T>;
+
+    T::timed_out(unsafe { &mut *p }) as bindings::drm_gpu_sched_stat
+}
+
+unsafe extern "C" fn free_job_cb<T: JobImpl>(sched_job: *mut bindings::drm_sched_job) {
+    // SAFETY: All of our jobs are Job<T>.
+    let p = crate::container_of!(sched_job, Job<T>, job) as *mut Job<T>;
+
+    // Convert the job back to a Box and drop it
+    // SAFETY: All of our Job<T>s are created inside a box.
+    unsafe { Box::from_raw(p) };
+}
+
+/// A DRM scheduler job.
+pub struct Job<T: JobImpl> {
+    job: bindings::drm_sched_job,
+    inner: T,
+}
+
+impl<T: JobImpl> Deref for Job<T> {
+    type Target = T;
+
+    fn deref(&self) -> &Self::Target {
+        &self.inner
+    }
+}
+
+impl<T: JobImpl> DerefMut for Job<T> {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        &mut self.inner
+    }
+}
+
+impl<T: JobImpl> Drop for Job<T> {
+    fn drop(&mut self) {
+        // SAFETY: At this point the job has either been submitted and this is being called from
+        // `free_job_cb` above, or it hasn't and it is safe to call `drm_sched_job_cleanup`.
+        unsafe { bindings::drm_sched_job_cleanup(&mut self.job) };
+    }
+}
+
+/// A pending DRM scheduler job (not yet armed)
+pub struct PendingJob<'a, T: JobImpl>(Box<Job<T>>, PhantomData<&'a T>);
+
+impl<'a, T: JobImpl> PendingJob<'a, T> {
+    /// Add a fence as a dependency to the job
+    pub fn add_dependency(&mut self, fence: Fence) -> Result {
+        to_result(unsafe {
+            bindings::drm_sched_job_add_dependency(&mut self.0.job, fence.into_raw())
+        })
+    }
+
+    /// Arm the job to make it ready for execution
+    pub fn arm(mut self) -> ArmedJob<'a, T> {
+        unsafe { bindings::drm_sched_job_arm(&mut self.0.job) };
+        ArmedJob(self.0, PhantomData)
+    }
+}
+
+impl<'a, T: JobImpl> Deref for PendingJob<'a, T> {
+    type Target = Job<T>;
+
+    fn deref(&self) -> &Self::Target {
+        &self.0
+    }
+}
+
+impl<'a, T: JobImpl> DerefMut for PendingJob<'a, T> {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        &mut self.0
+    }
+}
+
+/// An armed DRM scheduler job (not yet submitted)
+pub struct ArmedJob<'a, T: JobImpl>(Box<Job<T>>, PhantomData<&'a T>);
+
+impl<'a, T: JobImpl> ArmedJob<'a, T> {
+    /// Returns the job fences
+    pub fn fences(&self) -> JobFences<'_> {
+        JobFences(unsafe { &mut *self.0.job.s_fence })
+    }
+
+    /// Push the job for execution into the scheduler
+    pub fn push(self) {
+        // After this point, the job is submitted and owned by the scheduler
+        let ptr = match self {
+            ArmedJob(job, _) => Box::<Job<T>>::into_raw(job),
+        };
+
+        // SAFETY: We are passing in ownership of a valid Box raw pointer.
+        unsafe { bindings::drm_sched_entity_push_job(addr_of_mut!((*ptr).job)) };
+    }
+}
+impl<'a, T: JobImpl> Deref for ArmedJob<'a, T> {
+    type Target = Job<T>;
+
+    fn deref(&self) -> &Self::Target {
+        &self.0
+    }
+}
+
+impl<'a, T: JobImpl> DerefMut for ArmedJob<'a, T> {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        &mut self.0
+    }
+}
+
+/// Reference to the bundle of fences attached to a DRM scheduler job
+pub struct JobFences<'a>(&'a mut bindings::drm_sched_fence);
+
+impl<'a> JobFences<'a> {
+    /// Returns a new reference to the job scheduled fence.
+    pub fn scheduled(&mut self) -> Fence {
+        unsafe { Fence::get_raw(&mut self.0.scheduled) }
+    }
+
+    /// Returns a new reference to the job finished fence.
+    pub fn finished(&mut self) -> Fence {
+        unsafe { Fence::get_raw(&mut self.0.finished) }
+    }
+}
+
+struct EntityInner<T: JobImpl> {
+    entity: bindings::drm_sched_entity,
+    // TODO: Allow users to share guilty flag between entities
+    sched: Arc<SchedulerInner<T>>,
+    guilty: bindings::atomic_t,
+    _p: PhantomData<T>,
+}
+
+impl<T: JobImpl> Drop for EntityInner<T> {
+    fn drop(&mut self) {
+        // SAFETY: The EntityInner is initialized. This will cancel/free all jobs.
+        unsafe { bindings::drm_sched_entity_destroy(&mut self.entity) };
+    }
+}
+
+// SAFETY: TODO
+unsafe impl<T: JobImpl> Sync for EntityInner<T> {}
+unsafe impl<T: JobImpl> Send for EntityInner<T> {}
+
+/// A DRM scheduler entity.
+pub struct Entity<T: JobImpl>(Pin<Box<EntityInner<T>>>);
+
+impl<T: JobImpl> Entity<T> {
+    /// Create a new scheduler entity.
+    pub fn new(sched: &Scheduler<T>, priority: Priority) -> Result<Self> {
+        let mut entity: Box<MaybeUninit<EntityInner<T>>> = Box::try_new_zeroed()?;
+
+        let mut sched_ptr = &sched.0.sched as *const _ as *mut _;
+
+        // SAFETY: The Box is allocated above and valid.
+        unsafe {
+            bindings::drm_sched_entity_init(
+                addr_of_mut!((*entity.as_mut_ptr()).entity),
+                priority as _,
+                &mut sched_ptr,
+                1,
+                addr_of_mut!((*entity.as_mut_ptr()).guilty),
+            )
+        };
+
+        // SAFETY: The Box is allocated above and valid.
+        unsafe { addr_of_mut!((*entity.as_mut_ptr()).sched).write(sched.0.clone()) };
+
+        // SAFETY: entity is now initialized.
+        Ok(Self(Pin::from(unsafe { entity.assume_init() })))
+    }
+
+    /// Create a new job on this entity.
+    ///
+    /// The entity must outlive the pending job until it transitions into the submitted state,
+    /// after which the scheduler owns it.
+    pub fn new_job(&self, inner: T) -> Result<PendingJob<'_, T>> {
+        let mut job: Box<MaybeUninit<Job<T>>> = Box::try_new_zeroed()?;
+
+        // SAFETY: We hold a reference to the entity (which is a valid pointer),
+        // and the job object was just allocated above.
+        to_result(unsafe {
+            bindings::drm_sched_job_init(
+                addr_of_mut!((*job.as_mut_ptr()).job),
+                &self.0.as_ref().get_ref().entity as *const _ as *mut _,
+                core::ptr::null_mut(),
+            )
+        })?;
+
+        // SAFETY: The Box pointer is valid, and this initializes the inner member.
+        unsafe { addr_of_mut!((*job.as_mut_ptr()).inner).write(inner) };
+
+        // SAFETY: All fields of the Job<T> are now initialized.
+        Ok(PendingJob(unsafe { job.assume_init() }, PhantomData))
+    }
+}
+
+/// DRM scheduler inner data
+pub struct SchedulerInner<T: JobImpl> {
+    sched: bindings::drm_gpu_scheduler,
+    _p: PhantomData<T>,
+}
+
+impl<T: JobImpl> Drop for SchedulerInner<T> {
+    fn drop(&mut self) {
+        // SAFETY: The scheduler is valid. This assumes drm_sched_fini() will take care of
+        // freeing all in-progress jobs.
+        unsafe { bindings::drm_sched_fini(&mut self.sched) };
+    }
+}
+
+// SAFETY: TODO
+unsafe impl<T: JobImpl> Sync for SchedulerInner<T> {}
+unsafe impl<T: JobImpl> Send for SchedulerInner<T> {}
+
+/// A DRM Scheduler
+pub struct Scheduler<T: JobImpl>(Arc<SchedulerInner<T>>);
+
+impl<T: JobImpl> Scheduler<T> {
+    const OPS: bindings::drm_sched_backend_ops = bindings::drm_sched_backend_ops {
+        prepare_job: Some(prepare_job_cb::<T>),
+        can_run_job: Some(can_run_job_cb::<T>),
+        run_job: Some(run_job_cb::<T>),
+        timedout_job: Some(timedout_job_cb::<T>),
+        free_job: Some(free_job_cb::<T>),
+    };
+    /// Creates a new DRM Scheduler object
+    // TODO: Shared timeout workqueues & scores
+    pub fn new(
+        device: &impl device::RawDevice,
+        hw_submission: u32,
+        hang_limit: u32,
+        timeout_ms: usize,
+        name: &'static CStr,
+    ) -> Result<Scheduler<T>> {
+        let mut sched: UniqueArc<MaybeUninit<SchedulerInner<T>>> = UniqueArc::try_new_uninit()?;
+
+        // SAFETY: The drm_sched pointer is valid and pinned as it was just allocated above.
+        to_result(unsafe {
+            bindings::drm_sched_init(
+                addr_of_mut!((*sched.as_mut_ptr()).sched),
+                &Self::OPS,
+                hw_submission,
+                hang_limit,
+                bindings::msecs_to_jiffies(timeout_ms.try_into()?).try_into()?,
+                core::ptr::null_mut(),
+                core::ptr::null_mut(),
+                name.as_char_ptr(),
+                device.raw_device(),
+            )
+        })?;
+
+        // SAFETY: All fields of SchedulerInner are now initialized.
+        Ok(Scheduler(unsafe { sched.assume_init() }.into()))
+    }
+}

-- 
2.35.1