On Sat, Aug 23, 2025 at 5:48 AM Srinivasan Shanmugam
<srinivasan.shanmu...@amd.com> wrote:
>
> Enable userspace to obtain a handle to the kernel-owned MMIO_REMAP
> singleton when AMDGPU_GEM_DOMAIN_MMIO_REMAP is requested via
> amdgpu_gem_create_ioctl().
>
> Validate the fixed 4K constraint: if PAGE_SIZE > AMDGPU_GPU_PAGE_SIZE
> return -EINVAL; when provided, size and alignment must equal
> AMDGPU_GPU_PAGE_SIZE.
>
> If the singleton BO is not available, return -ENODEV.
>
> Cc: Christian König <christian.koe...@amd.com>
> Suggested-by: Alex Deucher <alexander.deuc...@amd.com>
> Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmu...@amd.com>
> ---
> drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c | 59 +++++++++++++++++++++++++
> 1 file changed, 59 insertions(+)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
> b/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
> index d8cffd26455b..655281f57a99 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
> @@ -424,6 +424,38 @@ const struct drm_gem_object_funcs
> amdgpu_gem_object_funcs = {
> .vm_ops = &amdgpu_gem_vm_ops,
> };
>
> +/**
> + * amdgpu_gem_get_mmio_remap_handle - Create a GEM handle for the MMIO_REMAP
> BO
> + * @file_priv: DRM file corresponding to the calling process
> + * @adev: amdgpu device
> + * @handle: returned userspace GEM handle (out)
> + *
> + * Creates a GEM handle to the kernel-owned singleton MMIO_REMAP buffer
> object
> + * (adev->rmmio_remap.bo). The BO is expected to be allocated during TTM init
> + * when the hardware exposes a remap base and PAGE_SIZE <= 4K.
> + *
> + * drm_gem_handle_create() acquires the handle reference, which will be
> dropped
> + * by GEM_CLOSE in userspace.
> + *
> + * * Return:
> + * * 0 on success
> + * * -ENODEV if the MMIO_REMAP BO is not available
> + * * A negative errno from drm_gem_handle_create() on failure
> + *
> + */
> +static int amdgpu_gem_get_mmio_remap_handle(struct drm_file *file_priv,
> + struct amdgpu_device *adev,
> + u32 *handle)
> +{
> + struct amdgpu_bo *bo = READ_ONCE(adev->rmmio_remap.bo);
Why are you using READ_ONCE here?
Alex
> +
> + if (!bo)
> + return -ENODEV;
> +
> + /* drm_gem_handle_create() gets the ref; GEM_CLOSE drops it */
> + return drm_gem_handle_create(file_priv, &bo->tbo.base, handle);
> +}
> +
> /*
> * GEM ioctls.
> */
> @@ -468,6 +500,33 @@ int amdgpu_gem_create_ioctl(struct drm_device *dev, void
> *data,
> if (args->in.domains & AMDGPU_GEM_DOMAIN_MMIO_REMAP)
> return -EINVAL;
>
> + /*
> + * === 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 ttm init.
> + */
> + if (args->in.domains & AMDGPU_GEM_DOMAIN_MMIO_REMAP) {
> + /*
> + * The MMIO remap page is fixed 4K on the GPU side. Do not
> + * allow use if the system PAGE_SIZE is larger than the GPU
> + * page size.
> + */
> + if (PAGE_SIZE > AMDGPU_GPU_PAGE_SIZE)
> + return -EINVAL;
> +
> + /* Enforce fixed size/alignment when provided by userspace. */
> + if (size && size != AMDGPU_GPU_PAGE_SIZE)
> + return -EINVAL;
> + if (args->in.alignment && args->in.alignment !=
> AMDGPU_GPU_PAGE_SIZE)
> + return -EINVAL;
> +
> + r = amdgpu_gem_get_mmio_remap_handle(filp, adev, &handle);
> + if (r)
> + return r;
> + args->out.handle = 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
>
