From de8955508b72f8a88afc3f2cbb62334d5f79ccc3 Mon Sep 17 00:00:00 2001 From: Srinivasan Shanmugam Date: Mon, 6 Oct 2025 19:46:53 +0530 Subject: [PATCH] drm/amdgpu/ttm: Pin 4K MMIO_REMAP Singleton BO at Init v2 MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit MMIO_REMAP (HDP flush page) is a hardware I/O window exposed via a PCI BAR. It must not migrate or be evicted. Allocate a single 4 KB GEM BO in AMDGPU_GEM_DOMAIN_MMIO_REMAP during TTM initialization when the hardware exposes a remap bus address and the host page size is <= 4 KiB. Reserve the BO and pin it at the TTM level so it remains fixed for its lifetime. No CPU mapping is established here. On teardown, reserve, unpin, and free the BO if present. This prepares the object to be shared (e.g., via dma-buf) without triggering placement changes or no CPU-access migration v2: Added extra NULL checks Suggested-by: Christian König Suggested-by: Alex Deucher Signed-off-by: Srinivasan Shanmugam Reviewed-by: Christian König Signed-off-by: Alex Deucher --- drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c | 32 +++++++++++++++++++++++++ 1 file changed, 32 insertions(+) diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c index 2b931e855abd9..ac67886acaa24 100644 --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c @@ -1820,6 +1820,10 @@ static void amdgpu_ttm_pools_fini(struct amdgpu_device *adev) * PAGE_SIZE is <= AMDGPU_GPU_PAGE_SIZE (4K). The BO is created as a regular * GEM object (amdgpu_bo_create). * + * The BO is created as a normal GEM object via amdgpu_bo_create(), then + * reserved and pinned at the TTM level (ttm_bo_pin()) so it can never be + * migrated or evicted. No CPU mapping is established here. + * * Return: * * 0 on success or intentional skip (feature not present/unsupported) * * negative errno on allocation failure @@ -1848,7 +1852,26 @@ static int amdgpu_ttm_mmio_remap_bo_init(struct amdgpu_device *adev) if (r) return r; + r = amdgpu_bo_reserve(adev->rmmio_remap.bo, true); + if (r) + goto err_unref; + + /* + * MMIO_REMAP is a fixed I/O placement (AMDGPU_PL_MMIO_REMAP). + * Use TTM-level pin so the BO cannot be evicted/migrated, + * independent of GEM domains. This + * enforces the “fixed I/O window” + */ + ttm_bo_pin(&adev->rmmio_remap.bo->tbo); + + amdgpu_bo_unreserve(adev->rmmio_remap.bo); return 0; + +err_unref: + if (adev->rmmio_remap.bo) + amdgpu_bo_unref(&adev->rmmio_remap.bo); + adev->rmmio_remap.bo = NULL; + return r; } /** @@ -1860,6 +1883,15 @@ static int amdgpu_ttm_mmio_remap_bo_init(struct amdgpu_device *adev) */ static void amdgpu_ttm_mmio_remap_bo_fini(struct amdgpu_device *adev) { + struct amdgpu_bo *bo = adev->rmmio_remap.bo; + + if (!bo) + return; /* <-- safest early exit */ + + if (!amdgpu_bo_reserve(adev->rmmio_remap.bo, true)) { + ttm_bo_unpin(&adev->rmmio_remap.bo->tbo); + amdgpu_bo_unreserve(adev->rmmio_remap.bo); + } amdgpu_bo_unref(&adev->rmmio_remap.bo); adev->rmmio_remap.bo = NULL; } -- 2.47.3