[PATCH] drm/amdgpu: improve debug VRAM access performance using sdma

[Jonathan Kim]

For better performance during VRAM access for debugged processes, do
read/write copies over SDMA.

In order to fulfill post mortem debugging on a broken device, fallback to
stable MMIO access when gpu recovery is disabled or when job submission
time outs are set to max.  Failed SDMA access should automatically fall
back to MMIO access.

Use a pre-allocated GTT bounce buffer pre-mapped into GART to avoid
page-table updates and TLB flushes on access.

Signed-off-by: Jonathan Kim <jonathan.kim at amd.com>
---
 drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c | 78 +++++++++++++++++++++++++
 drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.h |  5 +-
 2 files changed, 82 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
index 367abed1d6e6..512df4c09772 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
@@ -48,6 +48,7 @@
 #include <drm/ttm/ttm_range_manager.h>
 
 #include <drm/amdgpu_drm.h>
+#include <drm/drm_drv.h>
 
 #include "amdgpu.h"
 #include "amdgpu_object.h"
@@ -1429,6 +1430,70 @@ static void amdgpu_ttm_vram_mm_access(struct amdgpu_device *adev, loff_t pos,
 	}
 }
 
+static int amdgpu_ttm_access_memory_sdma(struct ttm_buffer_object *bo,
+					unsigned long offset, void *buf, int len, int write)
+{
+	struct amdgpu_bo *abo = ttm_to_amdgpu_bo(bo);
+	struct amdgpu_device *adev = amdgpu_ttm_adev(abo->tbo.bdev);
+	struct amdgpu_job *job;
+	struct dma_fence *fence;
+	uint64_t src_addr, dst_addr;
+	unsigned int num_dw;
+	int r, idx;
+
+	if (len != PAGE_SIZE)
+		return -EINVAL;
+
+	if (!adev->mman.sdma_access_ptr)
+		return -EACCES;
+
+	r = drm_dev_enter(adev_to_drm(adev), &idx);
+	if (r)
+		return r;
+
+	if (write)
+		memcpy(adev->mman.sdma_access_ptr, buf, len);
+
+	num_dw = ALIGN(adev->mman.buffer_funcs->copy_num_dw, 8);
+	r = amdgpu_job_alloc_with_ib(adev, num_dw * 4, AMDGPU_IB_POOL_DELAYED, &job);
+	if (r)
+		goto out;
+
+	src_addr = write ? amdgpu_bo_gpu_offset(adev->mman.sdma_access_bo) :
+			amdgpu_bo_gpu_offset(abo);
+	dst_addr = write ? amdgpu_bo_gpu_offset(abo) :
+			amdgpu_bo_gpu_offset(adev->mman.sdma_access_bo);
+	amdgpu_emit_copy_buffer(adev, &job->ibs[0], src_addr, dst_addr, PAGE_SIZE, false);
+
+	amdgpu_ring_pad_ib(adev->mman.buffer_funcs_ring, &job->ibs[0]);
+	WARN_ON(job->ibs[0].length_dw > num_dw);
+
+	r = amdgpu_job_submit(job, &adev->mman.entity, AMDGPU_FENCE_OWNER_UNDEFINED, &fence);
+	if (r) {
+		amdgpu_job_free(job);
+		goto out;
+	}
+
+	if (!dma_fence_wait_timeout(fence, false, adev->sdma_timeout))
+		r = -ETIMEDOUT;
+	dma_fence_put(fence);
+
+	if (!(r || write))
+		memcpy(buf, adev->mman.sdma_access_ptr, len);
+out:
+	drm_dev_exit(idx);
+	return r;
+}
+
+static inline bool amdgpu_ttm_allow_post_mortem_debug(struct amdgpu_device *adev)
+{
+	return amdgpu_gpu_recovery == 0 ||
+		adev->gfx_timeout == MAX_SCHEDULE_TIMEOUT ||
+		adev->compute_timeout == MAX_SCHEDULE_TIMEOUT ||
+		adev->sdma_timeout == MAX_SCHEDULE_TIMEOUT ||
+		adev->video_timeout == MAX_SCHEDULE_TIMEOUT;
+}
+
 /**
  * amdgpu_ttm_access_memory - Read or Write memory that backs a buffer object.
  *
@@ -1453,6 +1518,10 @@ static int amdgpu_ttm_access_memory(struct ttm_buffer_object *bo,
 	if (bo->resource->mem_type != TTM_PL_VRAM)
 		return -EIO;
 
+	if (!amdgpu_ttm_allow_post_mortem_debug(adev) &&
+			!amdgpu_ttm_access_memory_sdma(bo, offset, buf, len, write))
+		return len;
+
 	amdgpu_res_first(bo->resource, offset, len, &cursor);
 	while (cursor.remaining) {
 		size_t count, size = cursor.size;
@@ -1793,6 +1862,12 @@ int amdgpu_ttm_init(struct amdgpu_device *adev)
 		return r;
 	}
 
+	if (amdgpu_bo_create_kernel(adev, PAGE_SIZE, PAGE_SIZE,
+				AMDGPU_GEM_DOMAIN_GTT,
+				&adev->mman.sdma_access_bo, NULL,
+				adev->mman.sdma_access_ptr))
+		DRM_WARN("Debug VRAM access will use slowpath MM access\n");
+
 	return 0;
 }
 
@@ -1823,6 +1898,9 @@ void amdgpu_ttm_fini(struct amdgpu_device *adev)
 	ttm_range_man_fini(&adev->mman.bdev, AMDGPU_PL_OA);
 	ttm_device_fini(&adev->mman.bdev);
 	adev->mman.initialized = false;
+	if (adev->mman.sdma_access_ptr)
+		amdgpu_bo_free_kernel(&adev->mman.sdma_access_bo, NULL,
+					&adev->mman.sdma_access_ptr);
 	DRM_INFO("amdgpu: ttm finalized\n");
 }
 
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.h b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.h
index 91a087f9dc7c..b0116c4a768f 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.h
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.h
@@ -98,6 +98,10 @@ struct amdgpu_mman {
 	u64		fw_vram_usage_size;
 	struct amdgpu_bo	*fw_vram_usage_reserved_bo;
 	void		*fw_vram_usage_va;
+
+	/* PAGE_SIZE'd BO for process memory r/w over SDMA. */
+	struct amdgpu_bo	*sdma_access_bo;
+	void			*sdma_access_ptr;
 };
 
 struct amdgpu_copy_mem {
@@ -193,5 +197,4 @@ uint64_t amdgpu_ttm_tt_pte_flags(struct amdgpu_device *adev, struct ttm_tt *ttm,
 int amdgpu_ttm_evict_resources(struct amdgpu_device *adev, int mem_type);
 
 void amdgpu_ttm_debugfs_init(struct amdgpu_device *adev);
-
 #endif
-- 
2.25.1