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

[Boris Brezillon <boris.brezillon@collabora.com>]

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.

> +}
> +
> +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.

> +        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
> +            );
> +        }
> +    }
> +}