drm/i915: Dumb down the semaphore logic

While I think the previous code is correct, it was hard to follow and
hard to debug. Since we already have a ring abstraction, might as well
use it to handle the semaphore updates and compares.

I don't expect this code to make semaphores better or worse, but you
never know...

v2:
Remove magic per Keith's suggestions.
Ran Daniel's gem_ring_sync_loop test on this.

v3:
Ignored one of Keith's suggestions.

v4:
Removed some bloat per Daniel's recommendation.

Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Keith Packard <keithp@keithp.com>
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Signed-off-by: Keith Packard <keithp@keithp.com>

drivers/gpu/drm/i915/i915_gem_execbuffer.c

@@ -784,7 +784,8 @@ i915_gem_execbuffer_sync_rings(struct drm_i915_gem_object *obj,
 	}
 
 	from->sync_seqno[idx] = seqno;
-	return intel_ring_sync(to, from, seqno - 1);
+
+	return to->sync_to(to, from, seqno - 1);
 }
 
 static int

drivers/gpu/drm/i915/i915_reg.h

@@ -194,6 +194,13 @@
 #define  MI_SEMAPHORE_UPDATE	    (1<<21)
 #define  MI_SEMAPHORE_COMPARE	    (1<<20)
 #define  MI_SEMAPHORE_REGISTER	    (1<<18)
+#define  MI_SEMAPHORE_SYNC_RV	    (2<<16)
+#define  MI_SEMAPHORE_SYNC_RB	    (0<<16)
+#define  MI_SEMAPHORE_SYNC_VR	    (0<<16)
+#define  MI_SEMAPHORE_SYNC_VB	    (2<<16)
+#define  MI_SEMAPHORE_SYNC_BR	    (2<<16)
+#define  MI_SEMAPHORE_SYNC_BV	    (0<<16)
+#define  MI_SEMAPHORE_SYNC_INVALID  (1<<0)
 /*
  * 3D instructions used by the kernel
  */
@@ -296,6 +303,12 @@
 #define RING_CTL(base)		((base)+0x3c)
 #define RING_SYNC_0(base)	((base)+0x40)
 #define RING_SYNC_1(base)	((base)+0x44)
+#define GEN6_RVSYNC (RING_SYNC_0(RENDER_RING_BASE))
+#define GEN6_RBSYNC (RING_SYNC_1(RENDER_RING_BASE))
+#define GEN6_VRSYNC (RING_SYNC_1(GEN6_BSD_RING_BASE))
+#define GEN6_VBSYNC (RING_SYNC_0(GEN6_BSD_RING_BASE))
+#define GEN6_BRSYNC (RING_SYNC_0(BLT_RING_BASE))
+#define GEN6_BVSYNC (RING_SYNC_1(BLT_RING_BASE))
 #define RING_MAX_IDLE(base)	((base)+0x54)
 #define RING_HWS_PGA(base)	((base)+0x80)
 #define RING_HWS_PGA_GEN6(base)	((base)+0x2080)

drivers/gpu/drm/i915/intel_ringbuffer.c

@@ -315,79 +315,127 @@ static void render_ring_cleanup(struct intel_ring_buffer *ring)
 }
 
 static void
-update_semaphore(struct intel_ring_buffer *ring, int i, u32 seqno)
+update_mboxes(struct intel_ring_buffer *ring,
+	    u32 seqno,
+	    u32 mmio_offset)
 {
-	struct drm_device *dev = ring->dev;
-	struct drm_i915_private *dev_priv = dev->dev_private;
-	int id;
-
-	/*
-	 * cs -> 1 = vcs, 0 = bcs
-	 * vcs -> 1 = bcs, 0 = cs,
-	 * bcs -> 1 = cs, 0 = vcs.
-	 */
-	id = ring - dev_priv->ring;
-	id += 2 - i;
-	id %= 3;
-
-	intel_ring_emit(ring,
-			MI_SEMAPHORE_MBOX |
-			MI_SEMAPHORE_REGISTER |
-			MI_SEMAPHORE_UPDATE);
+	intel_ring_emit(ring, MI_SEMAPHORE_MBOX |
+			      MI_SEMAPHORE_GLOBAL_GTT |
+			      MI_SEMAPHORE_REGISTER |
+			      MI_SEMAPHORE_UPDATE);
 	intel_ring_emit(ring, seqno);
-	intel_ring_emit(ring,
-			RING_SYNC_0(dev_priv->ring[id].mmio_base) + 4*i);
+	intel_ring_emit(ring, mmio_offset);
 }
 
+/**
+ * gen6_add_request - Update the semaphore mailbox registers
+ * 
+ * @ring - ring that is adding a request
+ * @seqno - return seqno stuck into the ring
+ *
+ * Update the mailbox registers in the *other* rings with the current seqno.
+ * This acts like a signal in the canonical semaphore.
+ */
 static int
 gen6_add_request(struct intel_ring_buffer *ring,
-		 u32 *result)
+		 u32 *seqno)
 {
-	u32 seqno;
+	u32 mbox1_reg;
+	u32 mbox2_reg;
 	int ret;
 
 	ret = intel_ring_begin(ring, 10);
 	if (ret)
 		return ret;
 
-	seqno = i915_gem_get_seqno(ring->dev);
-	update_semaphore(ring, 0, seqno);
-	update_semaphore(ring, 1, seqno);
+	mbox1_reg = ring->signal_mbox[0];
+	mbox2_reg = ring->signal_mbox[1];
 
+	*seqno = i915_gem_get_seqno(ring->dev);
+
+	update_mboxes(ring, *seqno, mbox1_reg);
+	update_mboxes(ring, *seqno, mbox2_reg);
 	intel_ring_emit(ring, MI_STORE_DWORD_INDEX);
 	intel_ring_emit(ring, I915_GEM_HWS_INDEX << MI_STORE_DWORD_INDEX_SHIFT);
-	intel_ring_emit(ring, seqno);
+	intel_ring_emit(ring, *seqno);
 	intel_ring_emit(ring, MI_USER_INTERRUPT);
 	intel_ring_advance(ring);
 
-	*result = seqno;
 	return 0;
 }
 
-int
-intel_ring_sync(struct intel_ring_buffer *ring,
-		struct intel_ring_buffer *to,
+/**
+ * intel_ring_sync - sync the waiter to the signaller on seqno
+ *
+ * @waiter - ring that is waiting
+ * @signaller - ring which has, or will signal
+ * @seqno - seqno which the waiter will block on
+ */
+static int
+intel_ring_sync(struct intel_ring_buffer *waiter,
+		struct intel_ring_buffer *signaller,
+		int ring,
 		u32 seqno)
 {
 	int ret;
+	u32 dw1 = MI_SEMAPHORE_MBOX |
+		  MI_SEMAPHORE_COMPARE |
+		  MI_SEMAPHORE_REGISTER;
 
-	ret = intel_ring_begin(ring, 4);
+	ret = intel_ring_begin(waiter, 4);
 	if (ret)
 		return ret;
 
-	intel_ring_emit(ring,
-			MI_SEMAPHORE_MBOX |
-			MI_SEMAPHORE_REGISTER |
-			intel_ring_sync_index(ring, to) << 17 |
-			MI_SEMAPHORE_COMPARE);
-	intel_ring_emit(ring, seqno);
-	intel_ring_emit(ring, 0);
-	intel_ring_emit(ring, MI_NOOP);
-	intel_ring_advance(ring);
+	intel_ring_emit(waiter, dw1 | signaller->semaphore_register[ring]);
+	intel_ring_emit(waiter, seqno);
+	intel_ring_emit(waiter, 0);
+	intel_ring_emit(waiter, MI_NOOP);
+	intel_ring_advance(waiter);
 
 	return 0;
 }
 
+/* VCS->RCS (RVSYNC) or BCS->RCS (RBSYNC) */
+int
+render_ring_sync_to(struct intel_ring_buffer *waiter,
+		    struct intel_ring_buffer *signaller,
+		    u32 seqno)
+{
+	WARN_ON(signaller->semaphore_register[RCS] == MI_SEMAPHORE_SYNC_INVALID);
+	return intel_ring_sync(waiter,
+			       signaller,
+			       RCS,
+			       seqno);
+}
+
+/* RCS->VCS (VRSYNC) or BCS->VCS (VBSYNC) */
+int
+gen6_bsd_ring_sync_to(struct intel_ring_buffer *waiter,
+		      struct intel_ring_buffer *signaller,
+		      u32 seqno)
+{
+	WARN_ON(signaller->semaphore_register[VCS] == MI_SEMAPHORE_SYNC_INVALID);
+	return intel_ring_sync(waiter,
+			       signaller,
+			       VCS,
+			       seqno);
+}
+
+/* RCS->BCS (BRSYNC) or VCS->BCS (BVSYNC) */
+int
+gen6_blt_ring_sync_to(struct intel_ring_buffer *waiter,
+		      struct intel_ring_buffer *signaller,
+		      u32 seqno)
+{
+	WARN_ON(signaller->semaphore_register[BCS] == MI_SEMAPHORE_SYNC_INVALID);
+	return intel_ring_sync(waiter,
+			       signaller,
+			       BCS,
+			       seqno);
+}
+
+
+
 #define PIPE_CONTROL_FLUSH(ring__, addr__)					\
 do {									\
 	intel_ring_emit(ring__, GFX_OP_PIPE_CONTROL | PIPE_CONTROL_QW_WRITE |		\
@@ -1027,6 +1075,11 @@ static const struct intel_ring_buffer render_ring = {
 	.irq_put		= render_ring_put_irq,
 	.dispatch_execbuffer	= render_ring_dispatch_execbuffer,
 	.cleanup		= render_ring_cleanup,
+	.sync_to		= render_ring_sync_to,
+	.semaphore_register	= {MI_SEMAPHORE_SYNC_INVALID,
+				   MI_SEMAPHORE_SYNC_RV,
+				   MI_SEMAPHORE_SYNC_RB},
+	.signal_mbox		= {GEN6_VRSYNC, GEN6_BRSYNC},
 };
 
 /* ring buffer for bit-stream decoder */
@@ -1154,6 +1207,11 @@ static const struct intel_ring_buffer gen6_bsd_ring = {
 	.irq_get		= gen6_bsd_ring_get_irq,
 	.irq_put		= gen6_bsd_ring_put_irq,
 	.dispatch_execbuffer	= gen6_ring_dispatch_execbuffer,
+	.sync_to		= gen6_bsd_ring_sync_to,
+	.semaphore_register	= {MI_SEMAPHORE_SYNC_VR,
+				   MI_SEMAPHORE_SYNC_INVALID,
+				   MI_SEMAPHORE_SYNC_VB},
+	.signal_mbox		= {GEN6_RVSYNC, GEN6_BVSYNC},
 };
 
 /* Blitter support (SandyBridge+) */
@@ -1281,10 +1339,15 @@ static const struct intel_ring_buffer gen6_blt_ring = {
 	.flush			= blt_ring_flush,
 	.add_request		= gen6_add_request,
 	.get_seqno		= ring_get_seqno,
-	.irq_get			= blt_ring_get_irq,
-	.irq_put			= blt_ring_put_irq,
+	.irq_get		= blt_ring_get_irq,
+	.irq_put		= blt_ring_put_irq,
 	.dispatch_execbuffer	= gen6_ring_dispatch_execbuffer,
-	.cleanup			= blt_ring_cleanup,
+	.cleanup		= blt_ring_cleanup,
+	.sync_to		= gen6_blt_ring_sync_to,
+	.semaphore_register	= {MI_SEMAPHORE_SYNC_BR,
+				   MI_SEMAPHORE_SYNC_BV,
+				   MI_SEMAPHORE_SYNC_INVALID},
+	.signal_mbox		= {GEN6_RBSYNC, GEN6_VBSYNC},
 };
 
 int intel_init_render_ring_buffer(struct drm_device *dev)

drivers/gpu/drm/i915/intel_ringbuffer.h

@@ -75,7 +75,12 @@ struct  intel_ring_buffer {
 	int		(*dispatch_execbuffer)(struct intel_ring_buffer *ring,
 					       u32 offset, u32 length);
 	void		(*cleanup)(struct intel_ring_buffer *ring);
+	int		(*sync_to)(struct intel_ring_buffer *ring,
+				   struct intel_ring_buffer *to,
+				   u32 seqno);
 
+	u32		semaphore_register[3]; /*our mbox written by others */
+	u32		signal_mbox[2]; /* mboxes this ring signals to */
 	/**
 	 * List of objects currently involved in rendering from the
 	 * ringbuffer.
@@ -180,9 +185,6 @@ static inline void intel_ring_emit(struct intel_ring_buffer *ring,
 void intel_ring_advance(struct intel_ring_buffer *ring);
 
 u32 intel_ring_get_seqno(struct intel_ring_buffer *ring);
-int intel_ring_sync(struct intel_ring_buffer *ring,
-		    struct intel_ring_buffer *to,
-		    u32 seqno);
 
 int intel_init_render_ring_buffer(struct drm_device *dev);
 int intel_init_bsd_ring_buffer(struct drm_device *dev);