drm/radeon: Sync ME and PFP after CP semaphore waits v4

Fixes lockups due to CP read GPUVM faults when running piglit on Cape
Verde.

v2 (chk): apply the fix to R600+ as well, on CIK only the GFX CP has
a PFP, add more comments to R600 code, enable flushing again
v3: (agd5f): only apply to 7xx+. r6xx does not have the packet.
v4: (agd5f): split flush change into a separate patch, fix formatting

Signed-off-by: Michel Dänzer <[e-mail]>
Signed-off-by: Christian König <[e-mail]>
Signed-off-by: Alex Deucher <[e-mail]>
Tested-by: Michel Dänzer <[e-mail]>

drivers/gpu/drm/radeon/cik.c

···
 	radeon_ring_write(ring, 0);
 }
 
+/**
+ * cik_semaphore_ring_emit - emit a semaphore on the CP ring
+ *
+ * @rdev: radeon_device pointer
+ * @ring: radeon ring buffer object
+ * @semaphore: radeon semaphore object
+ * @emit_wait: Is this a sempahore wait?
+ *
+ * Emits a semaphore signal/wait packet to the CP ring and prevents the PFP
+ * from running ahead of semaphore waits.
+ */
 bool cik_semaphore_ring_emit(struct radeon_device *rdev,
 			     struct radeon_ring *ring,
 			     struct radeon_semaphore *semaphore,
···
 	radeon_ring_write(ring, PACKET3(PACKET3_MEM_SEMAPHORE, 1));
 	radeon_ring_write(ring, lower_32_bits(addr));
 	radeon_ring_write(ring, (upper_32_bits(addr) & 0xffff) | sel);
+
+	if (emit_wait && ring->idx == RADEON_RING_TYPE_GFX_INDEX) {
+		/* Prevent the PFP from running ahead of the semaphore wait */
+		radeon_ring_write(ring, PACKET3(PACKET3_PFP_SYNC_ME, 0));
+		radeon_ring_write(ring, 0x0);
+	}
 
 	return true;
 }

drivers/gpu/drm/radeon/r600.c

···
 	}
 }
 
+/**
+ * r600_semaphore_ring_emit - emit a semaphore on the CP ring
+ *
+ * @rdev: radeon_device pointer
+ * @ring: radeon ring buffer object
+ * @semaphore: radeon semaphore object
+ * @emit_wait: Is this a sempahore wait?
+ *
+ * Emits a semaphore signal/wait packet to the CP ring and prevents the PFP
+ * from running ahead of semaphore waits.
+ */
 bool r600_semaphore_ring_emit(struct radeon_device *rdev,
 			      struct radeon_ring *ring,
 			      struct radeon_semaphore *semaphore,
···
 	radeon_ring_write(ring, PACKET3(PACKET3_MEM_SEMAPHORE, 1));
 	radeon_ring_write(ring, lower_32_bits(addr));
 	radeon_ring_write(ring, (upper_32_bits(addr) & 0xff) | sel);
+
+	/* PFP_SYNC_ME packet only exists on 7xx+ */
+	if (emit_wait && (rdev->family >= CHIP_RV770)) {
+		/* Prevent the PFP from running ahead of the semaphore wait */
+		radeon_ring_write(ring, PACKET3(PACKET3_PFP_SYNC_ME, 0));
+		radeon_ring_write(ring, 0x0);
+	}
 
 	return true;
 }

drivers/gpu/drm/radeon/r600d.h

···
 		 */
 #              define PACKET3_CP_DMA_CMD_SAIC      (1 << 28)
 #              define PACKET3_CP_DMA_CMD_DAIC      (1 << 29)
+#define	PACKET3_PFP_SYNC_ME				0x42 /* r7xx+ only */
 #define	PACKET3_SURFACE_SYNC				0x43
 #              define PACKET3_CB0_DEST_BASE_ENA    (1 << 6)
 #              define PACKET3_FULL_CACHE_ENA       (1 << 20) /* r7xx+ only */