drm/radeon: update ib_execute for SI (v2)

When submitting a CONST_IB, emit a SWITCH_BUFFER
packet before the CONST_IB.  This isn't strictly necessary
(the driver will work fine without it), but is good practice
and allows for more flexible DE/CE sychronization options
in the future.  Current userspace drivers do not take
advantage of the CE yet.

v2: - clean up code flow a bit
    - no need to flush caches for CONST IB
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>

drivers/gpu/drm/radeon/si.c

@@ -1765,6 +1765,13 @@ void si_ring_ib_execute(struct radeon_device *rdev, struct radeon_ib *ib)
 	struct radeon_ring *ring = &rdev->ring[ib->ring];
 	u32 header;
 
+	if (ib->is_const_ib) {
+		/* set switch buffer packet before const IB */
+		radeon_ring_write(ring, PACKET3(PACKET3_SWITCH_BUFFER, 0));
+		radeon_ring_write(ring, 0);
+
+		header = PACKET3(PACKET3_INDIRECT_BUFFER_CONST, 2);
+	} else {
 		if (ring->rptr_save_reg) {
 			uint32_t next_rptr = ring->wptr + 3 + 4 + 8;
 			radeon_ring_write(ring, PACKET3(PACKET3_SET_CONFIG_REG, 1));
@@ -1773,10 +1780,8 @@ void si_ring_ib_execute(struct radeon_device *rdev, struct radeon_ib *ib)
 			radeon_ring_write(ring, next_rptr);
 		}
 
-	if (ib->is_const_ib)
-		header = PACKET3(PACKET3_INDIRECT_BUFFER_CONST, 2);
-	else
 		header = PACKET3(PACKET3_INDIRECT_BUFFER, 2);
+	}
 
 	radeon_ring_write(ring, header);
 	radeon_ring_write(ring,
@@ -1787,6 +1792,7 @@ void si_ring_ib_execute(struct radeon_device *rdev, struct radeon_ib *ib)
 	radeon_ring_write(ring, upper_32_bits(ib->gpu_addr) & 0xFFFF);
 	radeon_ring_write(ring, ib->length_dw | (ib->vm_id << 24));
 
+	if (!ib->is_const_ib) {
 		/* flush read cache over gart for this vmid */
 		radeon_ring_write(ring, PACKET3(PACKET3_SET_CONFIG_REG, 1));
 		radeon_ring_write(ring, (CP_COHER_CNTL2 - PACKET3_SET_CONFIG_REG_START) >> 2);
@@ -1799,6 +1805,7 @@ void si_ring_ib_execute(struct radeon_device *rdev, struct radeon_ib *ib)
 		radeon_ring_write(ring, 0xFFFFFFFF);
 		radeon_ring_write(ring, 0);
 		radeon_ring_write(ring, 10); /* poll interval */
+	}
 }
 
 /*

drivers/gpu/drm/radeon/sid.h

@@ -901,5 +901,6 @@
 #define	PACKET3_WAIT_ON_DE_COUNTER_DIFF			0x88
 #define	PACKET3_SET_CE_DE_COUNTERS			0x89
 #define	PACKET3_WAIT_ON_AVAIL_BUFFER			0x8A
+#define	PACKET3_SWITCH_BUFFER				0x8B
 
 #endif