[PATCH RFC 06/18] rust: drm: gem: shmem: Add DRM shmem helper abstraction

Asahi Lina
2023-03-07T14:32:29Z

The DRM shmem helper includes common code useful for drivers which
allocate GEM objects as anonymous shmem. Add a Rust abstraction for
this. Drivers can choose the raw GEM implementation or the shmem layer,
depending on their needs.

Signed-off-by: Asahi Lina <lina@asahilina.net>
---
drivers/gpu/drm/Kconfig | 5 +
rust/bindings/bindings_helper.h | 2 +
rust/helpers.c | 67 +++++++
rust/kernel/drm/gem/mod.rs | 3 +
rust/kernel/drm/gem/shmem.rs | 381 ++++++++++++++++++++++++++++++++++++++++
5 files changed, 458 insertions(+)

diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
index dab8f0f9aa96..70a983a17ac2 100644
--- a/drivers/gpu/drm/Kconfig
+++ b/drivers/gpu/drm/Kconfig
@@ -34,6 +34,11 @@ config RUST_DRM
bool "Rust support for the DRM subsystem"
depends on DRM=y

+config RUST_DRM_GEM_SHMEM_HELPER
+ bool
+ depends on RUST_DRM
+ select DRM_GEM_SHMEM_HELPER
+
config DRM_MIPI_DBI
tristate
depends on DRM
diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h
index 7183dfe6473f..9f152d373df8 100644
--- a/rust/bindings/bindings_helper.h
+++ b/rust/bindings/bindings_helper.h
@@ -10,6 +10,7 @@
#include <drm/drm_drv.h>
#include <drm/drm_file.h>
#include <drm/drm_gem.h>
+#include <drm/drm_gem_shmem_helper.h>
#include <drm/drm_ioctl.h>
#include <linux/delay.h>
#include <linux/device.h>
@@ -17,6 +18,7 @@
#include <linux/fs.h>
#include <linux/ioctl.h>
#include <linux/io-pgtable.h>
+#include <linux/iosys-map.h>
#include <linux/ktime.h>
#include <linux/of.h>
#include <linux/of_address.h>
diff --git a/rust/helpers.c b/rust/helpers.c
index 78ec4162b03b..388ff1100ea5 100644
--- a/rust/helpers.c
+++ b/rust/helpers.c
@@ -19,6 +19,7 @@
*/

#include <drm/drm_gem.h>
+#include <drm/drm_gem_shmem_helper.h>
#include <linux/bug.h>
#include <linux/build_bug.h>
#include <linux/device.h>
@@ -375,6 +376,18 @@ void rust_helper_init_completion(struct completion *c)
}
EXPORT_SYMBOL_GPL(rust_helper_init_completion);

+dma_addr_t rust_helper_sg_dma_address(const struct scatterlist *sg)
+{
+ return sg_dma_address(sg);
+}
+EXPORT_SYMBOL_GPL(rust_helper_sg_dma_address);
+
+int rust_helper_sg_dma_len(const struct scatterlist *sg)
+{
+ return sg_dma_len(sg);
+}
+EXPORT_SYMBOL_GPL(rust_helper_sg_dma_len);
+
#ifdef CONFIG_DRM

void rust_helper_drm_gem_object_get(struct drm_gem_object *obj)
@@ -395,6 +408,60 @@ __u64 rust_helper_drm_vma_node_offset_addr(struct drm_vma_offset_node *node)
}
EXPORT_SYMBOL_GPL(rust_helper_drm_vma_node_offset_addr);

+#ifdef CONFIG_DRM_GEM_SHMEM_HELPER
+
+void rust_helper_drm_gem_shmem_object_free(struct drm_gem_object *obj)
+{
+ return drm_gem_shmem_object_free(obj);
+}
+EXPORT_SYMBOL_GPL(rust_helper_drm_gem_shmem_object_free);
+
+void rust_helper_drm_gem_shmem_object_print_info(struct drm_printer *p, unsigned int indent,
+ const struct drm_gem_object *obj)
+{
+ drm_gem_shmem_object_print_info(p, indent, obj);
+}
+EXPORT_SYMBOL_GPL(rust_helper_drm_gem_shmem_object_print_info);
+
+int rust_helper_drm_gem_shmem_object_pin(struct drm_gem_object *obj)
+{
+ return drm_gem_shmem_object_pin(obj);
+}
+EXPORT_SYMBOL_GPL(rust_helper_drm_gem_shmem_object_pin);
+
+void rust_helper_drm_gem_shmem_object_unpin(struct drm_gem_object *obj)
+{
+ drm_gem_shmem_object_unpin(obj);
+}
+EXPORT_SYMBOL_GPL(rust_helper_drm_gem_shmem_object_unpin);
+
+struct sg_table *rust_helper_drm_gem_shmem_object_get_sg_table(struct drm_gem_object *obj)
+{
+ return drm_gem_shmem_object_get_sg_table(obj);
+}
+EXPORT_SYMBOL_GPL(rust_helper_drm_gem_shmem_object_get_sg_table);
+
+int rust_helper_drm_gem_shmem_object_vmap(struct drm_gem_object *obj,
+ struct iosys_map *map)
+{
+ return drm_gem_shmem_object_vmap(obj, map);
+}
+EXPORT_SYMBOL_GPL(rust_helper_drm_gem_shmem_object_vmap);
+
+void rust_helper_drm_gem_shmem_object_vunmap(struct drm_gem_object *obj,
+ struct iosys_map *map)
+{
+ drm_gem_shmem_object_vunmap(obj, map);
+}
+EXPORT_SYMBOL_GPL(rust_helper_drm_gem_shmem_object_vunmap);
+
+int rust_helper_drm_gem_shmem_object_mmap(struct drm_gem_object *obj, struct vm_area_struct *vma)
+{
+ return drm_gem_shmem_object_mmap(obj, vma);
+}
+EXPORT_SYMBOL_GPL(rust_helper_drm_gem_shmem_object_mmap);
+
+#endif
#endif

/*
diff --git a/rust/kernel/drm/gem/mod.rs b/rust/kernel/drm/gem/mod.rs
index 8a7d99613718..e66bdef35c2e 100644
--- a/rust/kernel/drm/gem/mod.rs
+++ b/rust/kernel/drm/gem/mod.rs
@@ -4,6 +4,9 @@
//!
//! C header: [`include/linux/drm/drm_gem.h`](../../../../include/linux/drm/drm_gem.h)

+#[cfg(CONFIG_RUST_DRM_GEM_SHMEM_HELPER)]
+pub mod shmem;
+
use alloc::boxed::Box;

use crate::{
diff --git a/rust/kernel/drm/gem/shmem.rs b/rust/kernel/drm/gem/shmem.rs
new file mode 100644
index 000000000000..15446ea1113e
--- /dev/null
+++ b/rust/kernel/drm/gem/shmem.rs
@@ -0,0 +1,381 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! DRM GEM shmem helper objects
+//!
+//! C header: [`include/linux/drm/drm_gem_shmem_helper.h`](../../../../include/linux/drm/drm_gem_shmem_helper.h)
+
+use crate::drm::{device, drv, gem};
+use crate::{
+ error::{from_kernel_err_ptr, to_result},
+ prelude::*,
+};
+use core::{
+ marker::PhantomData,
+ mem,
+ mem::{ManuallyDrop, MaybeUninit},
+ ops::{Deref, DerefMut},
+ ptr::addr_of_mut,
+ slice,
+};
+
+use gem::BaseObject;
+
+/// Trait which must be implemented by drivers using shmem-backed GEM objects.
+pub trait DriverObject: gem::BaseDriverObject<Object<Self>> {
+ /// Parent `Driver` for this object.
+ type Driver: drv::Driver;
+}
+
+// FIXME: This is terrible and I don't know how to avoid it
+#[cfg(CONFIG_NUMA)]
+macro_rules! vm_numa_fields {
+ ( $($field:ident: $val:expr),* $(,)? ) => {
+ bindings::vm_operations_struct {
+ $( $field: $val ),*,
+ set_policy: None,
+ get_policy: None,
+ }
+ }
+}
+
+#[cfg(not(CONFIG_NUMA))]
+macro_rules! vm_numa_fields {
+ ( $($field:ident: $val:expr),* $(,)? ) => {
+ bindings::vm_operations_struct {
+ $( $field: $val ),*
+ }
+ }
+}
+
+const SHMEM_VM_OPS: bindings::vm_operations_struct = vm_numa_fields! {
+ open: Some(bindings::drm_gem_shmem_vm_open),
+ close: Some(bindings::drm_gem_shmem_vm_close),
+ may_split: None,
+ mremap: None,
+ mprotect: None,
+ fault: Some(bindings::drm_gem_shmem_fault),
+ huge_fault: None,
+ map_pages: None,
+ pagesize: None,
+ page_mkwrite: None,
+ pfn_mkwrite: None,
+ access: None,
+ name: None,
+ find_special_page: None,
+};
+
+/// A shmem-backed GEM object.
+#[repr(C)]
+pub struct Object<T: DriverObject> {
+ obj: bindings::drm_gem_shmem_object,
+ // The DRM core ensures the Device exists as long as its objects exist, so we don't need to
+ // manage the reference count here.
+ dev: ManuallyDrop<device::Device<T::Driver>>,
+ inner: T,
+}
+
+unsafe extern "C" fn gem_create_object<T: DriverObject>(
+ raw_dev: *mut bindings::drm_device,
+ size: usize,
+) -> *mut bindings::drm_gem_object {
+ // SAFETY: GEM ensures the device lives as long as its objects live,
+ // so we can conjure up a reference from thin air and never drop it.
+ let dev = ManuallyDrop::new(unsafe { device::Device::from_raw(raw_dev) });
+
+ let inner = match T::new(&*dev, size) {
+ Ok(v) => v,
+ Err(e) => return e.to_ptr(),
+ };
+
+ let p = unsafe {
+ bindings::krealloc(
+ core::ptr::null(),
+ Object::<T>::SIZE,
+ bindings::GFP_KERNEL | bindings::__GFP_ZERO,
+ ) as *mut Object<T>
+ };
+
+ if p.is_null() {
+ return ENOMEM.to_ptr();
+ }
+
+ // SAFETY: p is valid as long as the alloc succeeded
+ unsafe {
+ addr_of_mut!((*p).dev).write(dev);
+ addr_of_mut!((*p).inner).write(inner);
+ }
+
+ // SAFETY: drm_gem_shmem_object is safe to zero-init, and
+ // the rest of Object has been initialized
+ let new: &mut Object<T> = unsafe { &mut *(p as *mut _) };
+
+ new.obj.base.funcs = &Object::<T>::VTABLE;
+ &mut new.obj.base
+}
+
+unsafe extern "C" fn free_callback<T: DriverObject>(obj: *mut bindings::drm_gem_object) {
+ // SAFETY: All of our objects are Object<T>.
+ let p = crate::container_of!(obj, Object<T>, obj) as *mut Object<T>;
+
+ // SAFETY: p is never used after this
+ unsafe {
+ core::ptr::drop_in_place(&mut (*p).inner);
+ }
+
+ // SAFETY: This pointer has to be valid, since p is valid
+ unsafe {
+ bindings::drm_gem_shmem_free(&mut (*p).obj);
+ }
+}
+
+impl<T: DriverObject> Object<T> {
+ /// The size of this object's structure.
+ const SIZE: usize = mem::size_of::<Self>();
+
+ /// `drm_gem_object_funcs` vtable suitable for GEM shmem objects.
+ const VTABLE: bindings::drm_gem_object_funcs = bindings::drm_gem_object_funcs {
+ free: Some(free_callback::<T>),
+ open: Some(super::open_callback::<T, Object<T>>),
+ close: Some(super::close_callback::<T, Object<T>>),
+ print_info: Some(bindings::drm_gem_shmem_object_print_info),
+ export: None,
+ pin: Some(bindings::drm_gem_shmem_object_pin),
+ unpin: Some(bindings::drm_gem_shmem_object_unpin),
+ get_sg_table: Some(bindings::drm_gem_shmem_object_get_sg_table),
+ vmap: Some(bindings::drm_gem_shmem_object_vmap),
+ vunmap: Some(bindings::drm_gem_shmem_object_vunmap),
+ mmap: Some(bindings::drm_gem_shmem_object_mmap),
+ vm_ops: &SHMEM_VM_OPS,
+ };
+
+ // SAFETY: Must only be used with DRM functions that are thread-safe
+ unsafe fn mut_shmem(&self) -> *mut bindings::drm_gem_shmem_object {
+ &self.obj as *const _ as *mut _
+ }
+
+ /// Create a new shmem-backed DRM object of the given size.
+ pub fn new(dev: &device::Device<T::Driver>, size: usize) -> Result<gem::UniqueObjectRef<Self>> {
+ // SAFETY: This function can be called as long as the ALLOC_OPS are set properly
+ // for this driver, and the gem_create_object is called.
+ let p = unsafe { bindings::drm_gem_shmem_create(dev.raw() as *mut _, size) };
+ let p = crate::container_of!(p, Object<T>, obj) as *mut _;
+
+ // SAFETY: The gem_create_object callback ensures this is a valid Object<T>,
+ // so we can take a unique reference to it.
+ let obj_ref = gem::UniqueObjectRef { ptr: p };
+
+ Ok(obj_ref)
+ }
+
+ /// Returns the `Device` that owns this GEM object.
+ pub fn dev(&self) -> &device::Device<T::Driver> {
+ &self.dev
+ }
+
+ /// Creates (if necessary) and returns a scatter-gather table of DMA pages for this object.
+ ///
+ /// This will pin the object in memory.
+ pub fn sg_table(&self) -> Result<SGTable<T>> {
+ // SAFETY: drm_gem_shmem_get_pages_sgt is thread-safe.
+ let sgt = from_kernel_err_ptr(unsafe {
+ bindings::drm_gem_shmem_get_pages_sgt(self.mut_shmem())
+ })?;
+
+ Ok(SGTable {
+ sgt,
+ _owner: self.reference(),
+ })
+ }
+
+ /// Creates and returns a virtual kernel memory mapping for this object.
+ pub fn vmap(&self) -> Result<VMap<T>> {
+ let mut map: MaybeUninit<bindings::iosys_map> = MaybeUninit::uninit();
+
+ // SAFETY: drm_gem_shmem_vmap is thread-safe
+ to_result(unsafe { bindings::drm_gem_shmem_vmap(self.mut_shmem(), map.as_mut_ptr()) })?;
+
+ // SAFETY: if drm_gem_shmem_vmap did not fail, map is initialized now
+ let map = unsafe { map.assume_init() };
+
+ Ok(VMap {
+ map,
+ owner: self.reference(),
+ })
+ }
+
+ /// Set the write-combine flag for this object.
+ ///
+ /// Should be called before any mappings are made.
+ pub fn set_wc(&mut self, map_wc: bool) {
+ unsafe { (*self.mut_shmem()).map_wc = map_wc };
+ }
+}
+
+impl<T: DriverObject> Deref for Object<T> {
+ type Target = T;
+
+ fn deref(&self) -> &Self::Target {
+ &self.inner
+ }
+}
+
+impl<T: DriverObject> DerefMut for Object<T> {
+ fn deref_mut(&mut self) -> &mut Self::Target {
+ &mut self.inner
+ }
+}
+
+impl<T: DriverObject> crate::private::Sealed for Object<T> {}
+
+impl<T: DriverObject> gem::IntoGEMObject for Object<T> {
+ type Driver = T::Driver;
+
+ fn gem_obj(&self) -> *mut bindings::drm_gem_object {
+ &self.obj.base as *const _ as *mut _
+ }
+
+ fn from_gem_obj(obj: *mut bindings::drm_gem_object) -> *mut Object<T> {
+ crate::container_of!(obj, Object<T>, obj) as *mut Object<T>
+ }
+}
+
+impl<T: DriverObject> drv::AllocImpl for Object<T> {
+ const ALLOC_OPS: drv::AllocOps = drv::AllocOps {
+ gem_create_object: Some(gem_create_object::<T>),
+ prime_handle_to_fd: Some(bindings::drm_gem_prime_handle_to_fd),
+ prime_fd_to_handle: Some(bindings::drm_gem_prime_fd_to_handle),
+ gem_prime_import: None,
+ gem_prime_import_sg_table: Some(bindings::drm_gem_shmem_prime_import_sg_table),
+ gem_prime_mmap: Some(bindings::drm_gem_prime_mmap),
+ dumb_create: Some(bindings::drm_gem_shmem_dumb_create),
+ dumb_map_offset: None,
+ dumb_destroy: None,
+ };
+}
+
+/// A virtual mapping for a shmem-backed GEM object in kernel address space.
+pub struct VMap<T: DriverObject> {
+ map: bindings::iosys_map,
+ owner: gem::ObjectRef<Object<T>>,
+}
+
+impl<T: DriverObject> VMap<T> {
+ /// Returns a const raw pointer to the start of the mapping.
+ pub fn as_ptr(&self) -> *const core::ffi::c_void {
+ // SAFETY: The shmem helpers always return non-iomem maps
+ unsafe { self.map.__bindgen_anon_1.vaddr }
+ }
+
+ /// Returns a mutable raw pointer to the start of the mapping.
+ pub fn as_mut_ptr(&mut self) -> *mut core::ffi::c_void {
+ // SAFETY: The shmem helpers always return non-iomem maps
+ unsafe { self.map.__bindgen_anon_1.vaddr }
+ }
+
+ /// Returns a byte slice view of the mapping.
+ pub fn as_slice(&self) -> &[u8] {
+ // SAFETY: The vmap maps valid memory up to the owner size
+ unsafe { slice::from_raw_parts(self.as_ptr() as *const u8, self.owner.size()) }
+ }
+
+ /// Returns mutable a byte slice view of the mapping.
+ pub fn as_mut_slice(&mut self) -> &mut [u8] {
+ // SAFETY: The vmap maps valid memory up to the owner size
+ unsafe { slice::from_raw_parts_mut(self.as_mut_ptr() as *mut u8, self.owner.size()) }
+ }
+
+ /// Borrows a reference to the object that owns this virtual mapping.
+ pub fn owner(&self) -> &gem::ObjectRef<Object<T>> {
+ &self.owner
+ }
+}
+
+impl<T: DriverObject> Drop for VMap<T> {
+ fn drop(&mut self) {
+ // SAFETY: This function is thread-safe
+ unsafe {
+ bindings::drm_gem_shmem_vunmap(self.owner.mut_shmem(), &mut self.map);
+ }
+ }
+}
+
+/// SAFETY: `iosys_map` objects are safe to send across threads.
+unsafe impl<T: DriverObject> Send for VMap<T> {}
+unsafe impl<T: DriverObject> Sync for VMap<T> {}
+
+/// A single scatter-gather entry, representing a span of pages in the device's DMA address space.
+///
+/// For devices not behind a standalone IOMMU, this corresponds to physical addresses.
+#[repr(transparent)]
+pub struct SGEntry(bindings::scatterlist);
+
+impl SGEntry {
+ /// Returns the starting DMA address of this span
+ pub fn dma_address(&self) -> usize {
+ (unsafe { bindings::sg_dma_address(&self.0) }) as usize
+ }
+
+ /// Returns the length of this span in bytes
+ pub fn dma_len(&self) -> usize {
+ (unsafe { bindings::sg_dma_len(&self.0) }) as usize
+ }
+}
+
+/// A scatter-gather table of DMA address spans for a GEM shmem object.
+///
+/// # Invariants
+/// `sgt` must be a valid pointer to the `sg_table`, which must correspond to the owned
+/// object in `_owner` (which ensures it remains valid).
+pub struct SGTable<T: DriverObject> {
+ sgt: *const bindings::sg_table,
+ _owner: gem::ObjectRef<Object<T>>,
+}
+
+impl<T: DriverObject> SGTable<T> {
+ /// Returns an iterator through the SGTable's entries
+ pub fn iter(&'_ self) -> SGTableIter<'_> {
+ SGTableIter {
+ left: unsafe { (*self.sgt).nents } as usize,
+ sg: unsafe { (*self.sgt).sgl },
+ _p: PhantomData,
+ }
+ }
+}
+
+impl<'a, T: DriverObject> IntoIterator for &'a SGTable<T> {
+ type Item = &'a SGEntry;
+ type IntoIter = SGTableIter<'a>;
+
+ fn into_iter(self) -> Self::IntoIter {
+ self.iter()
+ }
+}
+
+/// SAFETY: `sg_table` objects are safe to send across threads.
+unsafe impl<T: DriverObject> Send for SGTable<T> {}
+unsafe impl<T: DriverObject> Sync for SGTable<T> {}
+
+/// An iterator through `SGTable` entries.
+///
+/// # Invariants
+/// `sg` must be a valid pointer to the scatterlist, which must outlive our lifetime.
+pub struct SGTableIter<'a> {
+ sg: *mut bindings::scatterlist,
+ left: usize,
+ _p: PhantomData<&'a ()>,
+}
+
+impl<'a> Iterator for SGTableIter<'a> {
+ type Item = &'a SGEntry;
+
+ fn next(&mut self) -> Option<Self::Item> {
+ if self.left == 0 {
+ None
+ } else {
+ let sg = self.sg;
+ self.sg = unsafe { bindings::sg_next(self.sg) };
+ self.left -= 1;
+ Some(unsafe { &(*(sg as *const SGEntry)) })
+ }
+ }
+}

--
2.35.1