On Wed, Aug 20, 2025 at 7:43 AM Srinivasan Shanmugam
<srinivasan.shanmu...@amd.com> wrote:
>
> When userspace requests a GEM in AMDGPU_GEM_DOMAIN_MMIO_REMAP, return a
> handle to the kernel-owned singleton BO instead of allocating a new one.
>
> Validate inputs (exact PAGE_SIZE, alignment PAGE_SIZE, no extra flags)
> and zero the ioctl out-struct on success for a clean echo.
>
> This puts the userspace-visible behavior last, after all internal kernel
> plumbing and initialization are in place.
>
> Cc: Christian König <christian.koe...@amd.com>
> Cc: Alex Deucher <alexander.deuc...@amd.com>
> Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmu...@amd.com>
> ---
> drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c | 56 +++++++++++++++++++++++++
> 1 file changed, 56 insertions(+)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
> b/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
> index e3f65977eeee..1345e81214e8 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
> @@ -424,6 +424,26 @@ const struct drm_gem_object_funcs
> amdgpu_gem_object_funcs = {
> .vm_ops = &amdgpu_gem_vm_ops,
> };
>
> +/* ========= MMIO remap (HDP flush) GEM handle helper ========= */
> +static int amdgpu_gem_get_mmio_remap_handle(struct drm_file *file_priv,
> + struct amdgpu_device *adev,
> + u32 *handle)
> +{
> + struct amdgpu_bo *bo = adev->mmio_remap_bo;
> + struct drm_gem_object *gobj;
> + int r;
> +
> + if (!bo)
> + return -ENODEV;
> +
> + /* Take a temporary ref; the handle creation will hold its own ref. */
> + bo = amdgpu_bo_ref(bo);
> + gobj = &bo->tbo.base;
> + r = drm_gem_handle_create(file_priv, gobj, handle);
> + amdgpu_bo_unref(&bo); /* drops our temporary ref */
> + return r;
> +}
> +
> /*
> * GEM ioctls.
> */
> @@ -465,6 +485,42 @@ int amdgpu_gem_create_ioctl(struct drm_device *dev, void
> *data,
> /* always clear VRAM */
> flags |= AMDGPU_GEM_CREATE_VRAM_CLEARED;
>
> + /*
> + * === MMIO remap (HDP flush) fast-path ===
> + * If userspace asks for the MMIO_REMAP domain, don't allocate a new
> BO.
> + * Return a handle to the singleton BO created at device init.
> + */
> + if (args->in.domains & AMDGPU_GEM_DOMAIN_MMIO_REMAP) {
> + u32 mmio_handle;
Can drop this and just use handle from the top of this function.
> + /* Enforce fixed size & alignment (exactly one page). */
This needs to check that the PAGE_SIZE is 4K. E.g.,
If (PAGE_SIZE > 4096)
return -EINVAL;
Alex
> + if (size && size != PAGE_SIZE)
> + return -EINVAL;
> + if (args->in.alignment && args->in.alignment != PAGE_SIZE)
> + return -EINVAL;
> + /* No extra domain flags for this special object. */
> + if (args->in.domain_flags)
> + return -EINVAL;
> + /* Disallow flags that don't make sense for a fixed I/O page.
> */
> + if (flags & (AMDGPU_GEM_CREATE_CPU_GTT_USWC |
> + AMDGPU_GEM_CREATE_ENCRYPTED |
> + AMDGPU_GEM_CREATE_DISCARDABLE))
I think all flags would be irrelevant in this case.
> + return -EINVAL;
> +
> + /* Normalize inputs (optional, for user-visible echo/debug).
> */
> + args->in.bo_size = PAGE_SIZE;
> + args->in.alignment = PAGE_SIZE;
> + args->in.domains = AMDGPU_GEM_DOMAIN_MMIO_REMAP;
> + args->in.domain_flags = 0;
Why are you setting all of these?
Alex
> +
> + r = amdgpu_gem_get_mmio_remap_handle(filp, adev,
> &mmio_handle);
> + if (r)
> + return r;
> +
> + memset(args, 0, sizeof(*args));
> + args->out.handle = mmio_handle;
> + return 0;
> + }
> +
> /* create a gem object to contain this object in */
> if (args->in.domains & (AMDGPU_GEM_DOMAIN_GDS |
> AMDGPU_GEM_DOMAIN_GWS | AMDGPU_GEM_DOMAIN_OA)) {
> --
> 2.34.1
>
