drm/amdgpu: revert "take runtime pm reference when we attach a buffer" v2

This reverts commit b8c415e3bf98 ("drm/amdgpu: take runtime pm reference
when we attach a buffer") and commit 425285d39afd ("drm/amdgpu: add amdgpu
runpm usage trace for separate funcs").

Taking a runtime pm reference for DMA-buf is actually completely
unnecessary and even dangerous.

The problem is that calling pm_runtime_get_sync() from the DMA-buf
callbacks is illegal because we have the reservation locked here
which is also taken during resume. So this would deadlock.

When the buffer is in GTT it is still accessible even when the GPU
is powered down and when it is in VRAM the buffer gets migrated to
GTT before powering down.

The only use case which would make it mandatory to keep the runtime
pm reference would be if we pin the buffer into VRAM, and that's not
something we currently do.

v2: improve the commit message

Signed-off-by: Christian König <[e-mail]>
Reviewed-by: Alex Deucher <[e-mail]>
Signed-off-by: Alex Deucher <[e-mail]>
CC: [e-mail]

drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c

···
 #include <linux/dma-buf.h>
 #include <linux/dma-fence-array.h>
 #include <linux/pci-p2pdma.h>
-#include <linux/pm_runtime.h>
-#include "amdgpu_trace.h"
 
 /**
  * amdgpu_dma_buf_attach - &dma_buf_ops.attach implementation
···
 	struct drm_gem_object *obj = dmabuf->priv;
 	struct amdgpu_bo *bo = gem_to_amdgpu_bo(obj);
 	struct amdgpu_device *adev = amdgpu_ttm_adev(bo->tbo.bdev);
-	int r;
 
 	if (pci_p2pdma_distance(adev->pdev, attach->dev, false) < 0)
 		attach->peer2peer = false;
 
-	r = pm_runtime_get_sync(adev_to_drm(adev)->dev);
-	trace_amdgpu_runpm_reference_dumps(1, __func__);
-	if (r < 0)
-		goto out;
-
 	return 0;
-
-out:
-	pm_runtime_put_autosuspend(adev_to_drm(adev)->dev);
-	trace_amdgpu_runpm_reference_dumps(0, __func__);
-	return r;
-}
-
-/**
- * amdgpu_dma_buf_detach - &dma_buf_ops.detach implementation
- *
- * @dmabuf: DMA-buf where we remove the attachment from
- * @attach: the attachment to remove
- *
- * Called when an attachment is removed from the DMA-buf.
- */
-static void amdgpu_dma_buf_detach(struct dma_buf *dmabuf,
-				  struct dma_buf_attachment *attach)
-{
-	struct drm_gem_object *obj = dmabuf->priv;
-	struct amdgpu_bo *bo = gem_to_amdgpu_bo(obj);
-	struct amdgpu_device *adev = amdgpu_ttm_adev(bo->tbo.bdev);
-
-	pm_runtime_mark_last_busy(adev_to_drm(adev)->dev);
-	pm_runtime_put_autosuspend(adev_to_drm(adev)->dev);
-	trace_amdgpu_runpm_reference_dumps(0, __func__);
 }
 
 /**
···
 
 const struct dma_buf_ops amdgpu_dmabuf_ops = {
 	.attach = amdgpu_dma_buf_attach,
-	.detach = amdgpu_dma_buf_detach,
 	.pin = amdgpu_dma_buf_pin,
 	.unpin = amdgpu_dma_buf_unpin,
 	.map_dma_buf = amdgpu_dma_buf_map,

drivers/gpu/drm/amd/amdgpu/amdgpu_fence.c

···
 	amdgpu_ring_emit_fence(ring, ring->fence_drv.gpu_addr,
 			       seq, flags | AMDGPU_FENCE_FLAG_INT);
 	pm_runtime_get_noresume(adev_to_drm(adev)->dev);
-	trace_amdgpu_runpm_reference_dumps(1, __func__);
 	ptr = &ring->fence_drv.fences[seq & ring->fence_drv.num_fences_mask];
 	if (unlikely(rcu_dereference_protected(*ptr, 1))) {
 		struct dma_fence *old;
···
 		dma_fence_put(fence);
 		pm_runtime_mark_last_busy(adev_to_drm(adev)->dev);
 		pm_runtime_put_autosuspend(adev_to_drm(adev)->dev);
-		trace_amdgpu_runpm_reference_dumps(0, __func__);
 	} while (last_seq != seq);
 
 	return true;

drivers/gpu/drm/amd/amdgpu/amdgpu_trace.h

···
 		      __entry->value)
 );
 
-TRACE_EVENT(amdgpu_runpm_reference_dumps,
-	    TP_PROTO(uint32_t index, const char *func),
-	    TP_ARGS(index, func),
-	    TP_STRUCT__entry(
-			     __field(uint32_t, index)
-			     __string(func, func)
-			     ),
-	    TP_fast_assign(
-			   __entry->index = index;
-			   __assign_str(func);
-			   ),
-	    TP_printk("amdgpu runpm reference dump 0x%x: 0x%s\n",
-		      __entry->index,
-		      __get_str(func))
-);
 #undef AMDGPU_JOB_GET_TIMELINE_NAME
 #endif