> On 14 Jul 2026, at 00:18, Deborah Brouwer <[email protected]>
> wrote:
>
> Introduce a buffer object type (KernelBo) for internal driver allocations
> that are managed by the kernel rather than userspace.
>
> KernelBo wraps a GEM shmem object and automatically handles GPU virtual
> address space mapping during creation and unmapping on drop. This provides
> a safe and convenient way for the driver to both allocate and clean up
> internal buffers for kernel-managed resources.
>
> Co-developed-by: Boris Brezillon <[email protected]>
> Signed-off-by: Boris Brezillon <[email protected]>
> Signed-off-by: Deborah Brouwer <[email protected]>
> ---
> drivers/gpu/drm/tyr/gem.rs | 101 +++++++++++++++++++++++++++++++++++++++++++--
> 1 file changed, 97 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/tyr/gem.rs b/drivers/gpu/drm/tyr/gem.rs
> index c28be61a01bb..47a05a33388e 100644
> --- a/drivers/gpu/drm/tyr/gem.rs
> +++ b/drivers/gpu/drm/tyr/gem.rs
> @@ -4,18 +4,29 @@
> //! This module provides buffer object (BO) management functionality using
> //! DRM's GEM subsystem with shmem backing.
>
> +use core::ops::Range;
> +
> use kernel::{
> drm::gem::{
> self,
> shmem, //
> },
> prelude::*,
> - sync::aref::ARef, //
> + sync::{
> + aref::ARef,
> + Arc, //
> + }, //
> };
>
> -use crate::driver::{
> - TyrDrmDevice,
> - TyrDrmDriver, //
> +use crate::{
> + driver::{
> + TyrDrmDevice,
> + TyrDrmDriver, //
> + },
> + vm::{
> + Vm,
> + VmMapFlags, //
> + },
> };
>
> /// Tyr's DriverObject type for GEM objects.
> @@ -56,3 +67,85 @@ pub(crate) fn new_dummy_object(ddev: &TyrDrmDevice) ->
> Result<ARef<Bo>> {
>
> Ok(bo)
> }
> +
> +/// Specifies how to choose a GPU virtual address for a [`KernelBo`].
> +/// An automatic VA allocation strategy will be added in the future.
> +pub(crate) enum KernelBoVaAlloc {
> + /// Explicit VA address specified by the caller.
> + #[expect(dead_code)]
> + Explicit(u64),
> +}
> +
> +/// A kernel-owned buffer object with automatic GPU virtual address mapping.
> +///
> +/// This structure represents a buffer object that is created and managed
> entirely
> +/// by the kernel driver, as opposed to userspace-created GEM objects. It
> combines
> +/// a GEM object with automatic GPU virtual address (VA) space mapping and
> cleanup.
> +///
> +/// When dropped, the buffer is automatically unmapped from the GPU VA space.
> +pub(crate) struct KernelBo<'bound> {
> + /// The underlying GEM buffer object.
> + #[expect(dead_code)]
> + pub(crate) bo: ARef<Bo>,
Can we make this private?
> + /// The GPU VM this buffer is mapped into.
> + vm: Arc<Vm<'bound>>,
> + /// The GPU VA range occupied by this buffer.
> + va_range: Range<u64>,
> +}
> +
> +impl<'bound> KernelBo<'bound> {
> + /// Creates a new kernel-owned buffer object and maps it into GPU VA
> space.
> + ///
> + /// This function allocates a new shmem-backed GEM object and
> immediately maps
> + /// it into the specified GPU virtual memory space. The mapping is
> automatically
> + /// cleaned up when the [`KernelBo`] is dropped.
> + #[expect(dead_code)]
> + pub(crate) fn new(
> + ddev: &TyrDrmDevice,
> + vm: Arc<Vm<'bound>>,
> + size: u64,
> + va_alloc: KernelBoVaAlloc,
> + flags: VmMapFlags,
> + ) -> Result<Self> {
> + if size == 0 {
> + pr_err!("Cannot create KernelBo with size 0\n");
> + return Err(EINVAL);
> + }
> +
> + let KernelBoVaAlloc::Explicit(va) = va_alloc;
> +
> + let bo = Bo::new(
> + ddev,
> + size as usize,
As a general rule, let’s try our best to reduce the number of `as` casts. Let’s
go with
usize::try_from
> + shmem::ObjectConfig {
> + map_wc: true,
> + parent_resv_obj: None,
> + },
> + BoCreateArgs { flags: 0 },
> + )?;
> +
> + vm.map_bo_range(&bo, 0, size, va, flags)?;
> +
> + Ok(KernelBo {
> + bo,
> + vm,
> + va_range: va..(va + size),
> + })
> + }
> +}
> +
> +impl Drop for KernelBo<'_> {
> + fn drop(&mut self) {
> + let va = self.va_range.start;
> + let size = self.va_range.end - self.va_range.start;
> +
> + if let Err(e) = self.vm.unmap_range(va, size) {
> + pr_err!(
> + "Failed to unmap KernelBo range {:#x}..{:#x}: {:?}\n",
> + self.va_range.start,
> + self.va_range.end,
> + e
> + );
> + }
> + }
> +}
>
> --
> 2.54.0
>
