Re: [PATCH 10/12] drm/tyr: add a kernel buffer object

[Deborah Brouwer <deborah.brouwer@collabora.com>]

On Thu, Feb 12, 2026 at 12:00:43PM +0100, Boris Brezillon wrote:
> On Wed, 11 Feb 2026 17:37:11 -0800
> Deborah Brouwer <deborah.brouwer@collabora.com> 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 <boris.brezillon@collabora.com>
> > Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
> > Signed-off-by: Deborah Brouwer <deborah.brouwer@collabora.com>
> > ---
> >  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
> > +            );
> > +        }
> > +    }
> > +}
>