[RFC PATCH 6/7] drm/amdgpu: Create Singleton MMIO_REMAP BO and Initialize its pool

[Alex Deucher]

On Wed, Aug 20, 2025 at 7:33 AM Srinivasan Shanmugam
<srinivasan.shanmugam at amd.com> wrote:
>
> Create the single-page MMIO_REMAP BO and initialize a tiny on-chip
> range manager for the new placement:
>
> * add amdgpu_mmio_remap_bo_init()/fini()
> * in amdgpu_ttm_init(): initialize AMDGPU_PL_MMIO_REMAP heap and create
>   the PAGE_SIZE BO
> * in amdgpu_ttm_fini(): drop BO and tear down the range manager
>
> This isolates lifetime management and error paths for the remap BO and
> ties them into the TTM bring-up/teardown flow.
>
> Cc: Christian König <christian.koenig at amd.com>
> Cc: Alex Deucher <alexander.deucher at amd.com>
> Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmugam at amd.com>
> ---
>  drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c | 86 +++++++++++++++++++++++++
>  1 file changed, 86 insertions(+)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
> index 157a5416a826..ab93fbec2a34 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
> @@ -1859,6 +1859,73 @@ static void amdgpu_ttm_pools_fini(struct amdgpu_device *adev)
>         adev->mman.ttm_pools = NULL;
>  }
>
> +/* ================= MMIO remap (HDP flush) singleton BO ================= */
> +static int amdgpu_mmio_remap_bo_init(struct amdgpu_device *adev)

Prefix this function with amdgpu_ttm_ for consistency.

> +{
> +       resource_size_t bar_base, bar_len, bus, off;
> +       int r;
> +
> +       /* The ASIC code should have set this to the absolute bus address
> +        * of the remap page (inside the register BAR).
> +        */
> +       bus = adev->rmmio_remap.bus_addr;

Just remove adev->rmmio_remap.bus_addr and use the new
adev->mmio_remap.base that you added.  We don't need two copies.

if the base is 0, then we can just return 0 here.  We can't allocate
the buffer if the PAGE_SIZE is > 4K.

> +       if (!bus) {
> +               dev_dbg(adev->dev, "MMIO_REMAP: no remap bus addr; skipping BO\n");
> +               return -ENODEV;
> +       }
> +
> +       /* The register BAR base/size were established in amdgpu_device_init() */
> +       bar_base = adev->rmmio_base;
> +       bar_len  = adev->rmmio_size;
> +
> +       /* Sanity: page must lie wholly inside the register BAR */
> +       if (bus < bar_base || (bus + PAGE_SIZE) > (bar_base + bar_len)) {
> +               dev_err(adev->dev,
> +                       "MMIO_REMAP: bus 0x%llx not in REG BAR [0x%llx..0x%llx)\n",
> +                       (unsigned long long)bus,
> +                       (unsigned long long)bar_base,
> +                       (unsigned long long)(bar_base + bar_len));
> +               return -ERANGE;
> +       }
> +
> +       off = bus - bar_base;
> +       if (!IS_ALIGNED(off, PAGE_SIZE)) {
> +               dev_err(adev->dev, "MMIO_REMAP: offset 0x%llx not page-aligned\n",
> +                       (unsigned long long)off);
> +               return -EINVAL;
> +       }

All of this can be dropped.

> +
> +       /* Create exactly ONE kernel-owned BO in the MMIO_REMAP domain */
> +       r = amdgpu_bo_create_kernel(adev,
> +                                   PAGE_SIZE,                 /* bo_size  */
> +                                   PAGE_SIZE,                 /* alignment*/
> +                                   AMDGPU_GEM_DOMAIN_MMIO_REMAP,
> +                                   &adev->mmio_remap_bo,
> +                                   NULL, NULL);

You can probably just call this directly below rather than adding a
wrapper function.

> +       if (r) {
> +               dev_err(adev->dev, "MMIO_REMAP: BO create failed (%d)\n", r);
> +               return r;
> +       }
> +
> +       dev_dbg(adev->dev,
> +               "MMIO_REMAP: base=0x%llx off=0x%llx size=0x%lx (BO created)\n",
> +               (unsigned long long)adev->mmio_remap_base,
> +               (unsigned long long)adev->mmio_remap_offset,
> +               (unsigned long)adev->mmio_remap_size);
> +
> +       return 0;
> +}
> +
> +static void amdgpu_mmio_remap_bo_fini(struct amdgpu_device *adev)
> +{
> +
> +       if (adev->mmio_remap_bo)
> +               amdgpu_bo_free_kernel(&adev->mmio_remap_bo, NULL, NULL);
> +       adev->mmio_remap_bo = NULL;

Same here.

> +
> +       return;
> +}
> +
>  /*
>   * amdgpu_ttm_init - Init the memory management (ttm) as well as various
>   * gtt/vram related fields.
> @@ -2026,6 +2093,20 @@ int amdgpu_ttm_init(struct amdgpu_device *adev)
>                 return r;
>         }
>
> +       /* Initialize MMIO-remap pool (single page) */
> +       r = amdgpu_ttm_init_on_chip(adev, AMDGPU_PL_MMIO_REMAP, 1);
> +       if (r) {
> +               dev_err(adev->dev, "Failed initializing MMIO-remap heap.\n");
> +               return r;
> +       }
> +
> +       /* Create the singleton MMIO-remap BO (one page) */
> +       r = amdgpu_mmio_remap_bo_init(adev);
> +       if (r) {
> +               dev_err(adev->dev, "Failed to create MMIO-remap singleton BO.\n");
> +               return r;
> +       }

This could be split into a separate patch.  One patch to create the
heap and a separate patch to allocate the BO.

> +
>         /* Initialize preemptible memory pool */
>         r = amdgpu_preempt_mgr_init(adev);
>         if (r) {
> @@ -2088,6 +2169,9 @@ void amdgpu_ttm_fini(struct amdgpu_device *adev)
>         }
>         amdgpu_bo_free_kernel(&adev->mman.sdma_access_bo, NULL,
>                                         &adev->mman.sdma_access_ptr);
> +
> +       /* === Drop the singleton MMIO-remap BO === */

Drop this comment.

> +       amdgpu_mmio_remap_bo_fini(adev);
>         amdgpu_ttm_fw_reserve_vram_fini(adev);
>         amdgpu_ttm_drv_reserve_vram_fini(adev);
>
> @@ -2109,6 +2193,8 @@ void amdgpu_ttm_fini(struct amdgpu_device *adev)
>         ttm_range_man_fini(&adev->mman.bdev, AMDGPU_PL_GWS);
>         ttm_range_man_fini(&adev->mman.bdev, AMDGPU_PL_OA);
>         ttm_range_man_fini(&adev->mman.bdev, AMDGPU_PL_DOORBELL);
> +       /* Tear down the tiny range manager for MMIO-remap */

Drop this comment.

Alex

> +       ttm_range_man_fini(&adev->mman.bdev, AMDGPU_PL_MMIO_REMAP);
>         ttm_device_fini(&adev->mman.bdev);
>         adev->mman.initialized = false;
>         dev_info(adev->dev, "amdgpu: ttm finalized\n");
> --
> 2.34.1
>