On Thu, Feb 12, 2026 at 12:00:43PM +0100, Boris Brezillon wrote:
> On Wed, 11 Feb 2026 17:37:11 -0800
> 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 | 74 +++++++++++++++++++++++++++++++++++---
> > 1 file changed, 70 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/tyr/gem.rs b/drivers/gpu/drm/tyr/gem.rs
> > index 111acf33993f..3807810be7ea 100644
> > --- a/drivers/gpu/drm/tyr/gem.rs
> > +++ b/drivers/gpu/drm/tyr/gem.rs
> > @@ -4,6 +4,8 @@
> > //! This module provides buffer object (BO) management functionality using
> > //! DRM's GEM subsystem with shmem backing.
> >
> > +use core::ops::Range;
> > +
> > use kernel::{
> > drm::{
> > gem,
> > @@ -11,12 +13,22 @@
> > DeviceContext, //
> > },
> > prelude::*,
> > - sync::aref::ARef, //
> > + sync::{
> > + aref::ARef,
> > + Arc,
> > + ArcBorrow, //
> > + },
> > };
> >
> > -use crate::driver::{
> > - TyrDrmDevice,
> > - TyrDrmDriver, //
> > +use crate::{
> > + driver::{
> > + TyrDrmDevice,
> > + TyrDrmDriver, //
> > + },
> > + vm::{
> > + Vm,
> > + VmMapFlags, //
> > + },
> > };
> >
> > /// Tyr's DriverObject type for GEM objects.
> > @@ -61,3 +73,57 @@ pub(crate) fn new_dummy_object<Ctx: DeviceContext>(ddev:
> > &TyrDrmDevice<Ctx>) ->
> >
> > Ok(bo)
> > }
> > +
> > +/// A buffer object that is owned and managed by Tyr rather than userspace.
> > +pub(crate) struct KernelBo {
> > + #[expect(dead_code)]
> > + pub(crate) bo: ARef<Bo>,
> > + vm: Arc<Vm>,
> > + va_range: Range<u64>,
>
> Missing docs for all those fields.
Ack.
>
> > +}
> > +
> > +impl KernelBo {
> > + /// Creates a new kernel-owned buffer object and maps it into GPU VA
> > space.
> > + #[expect(dead_code)]
> > + pub(crate) fn new<Ctx: DeviceContext>(
> > + ddev: &TyrDrmDevice<Ctx>,
> > + vm: ArcBorrow<'_, Vm>,
> > + size: u64,
> > + va: u64,
>
> I'm already thinking about the next step (automatic VA-range
> allocation), and I'd be tempted to go directly for:
>
> enum KernelBoVaAlloc {
> Explicit(u64),
> }
>
> so we can easily extend it with
>
> enum KernelBoVaAlloc {
> Auto,
> Explicit(u64),
> }
>
> when we have to.
>
Sure that is easily done.
> > + flags: VmMapFlags,
> > + ) -> Result<Self> {
> > + let bo = gem::shmem::Object::<BoData>::new(
> > + ddev,
> > + size as usize,
> > + 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: vm.into(),
> > + 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
> > + );
> > + }
> > + }
> > +}
>
