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

[Christian König]

On 20.08.25 13:32, Srinivasan Shanmugam 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 ================= */

Please drop those =, either use kerneldoc a just a comment.

> +static int amdgpu_mmio_remap_bo_init(struct amdgpu_device *adev)
> +{
> +	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;
> +	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;
> +	}
> +

Please drop all that. The code here should not check anything but just creates the BO at the specific location.

> +	/* 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);

That won't work like this. The difference between a kernel and an userspace BO is that kernel BOs can't be mapped into userspace.

You need to use amdgpu_bo_create() here, lock it and kmap it manually.

> +	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)

Drop that check.

Regards,
Christian.

> +		amdgpu_bo_free_kernel(&adev->mmio_remap_bo, NULL, NULL);
> +	adev->mmio_remap_bo = NULL;
> +
> +	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;
> +	}
> +
>  	/* 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 === */
> +	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 */
> +	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");