drm/i915: Move all ring resets before setting the HWS page

In commit a51435a313
Author: Naresh Kumar Kachhi <naresh.kumar.kachhi@intel.com>
Date:   Wed Mar 12 16:39:40 2014 +0530

    drm/i915: disable rings before HW status page setup

we reordered stopping the rings to do so before we set the HWS register.
However, there is an extra workaround for g45 to reset the rings twice,
and for consistency we should apply that workaround before setting the
HWS to be sure that the rings are truly stopped.

Reference: http://lkml.kernel.org/r/20140423202248.GA3621@amd.pavel.ucw.cz
Tested-by: Pavel Machek <pavel@ucw.cz>
Cc: Naresh Kumar Kachhi <naresh.kumar.kachhi@intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>

drivers/gpu/drm/i915/i915_reg.h

@@ -827,6 +827,7 @@ enum punit_power_well {
 # define MI_FLUSH_ENABLE				(1 << 12)
 # define ASYNC_FLIP_PERF_DISABLE			(1 << 14)
 # define MODE_IDLE					(1 << 9)
+# define STOP_RING					(1 << 8)
 
 #define GEN6_GT_MODE	0x20d0
 #define GEN7_GT_MODE	0x7008

drivers/gpu/drm/i915/intel_ringbuffer.c

@@ -437,32 +437,41 @@ static void ring_setup_phys_status_page(struct intel_ring_buffer *ring)
 	I915_WRITE(HWS_PGA, addr);
 }
 
+static bool stop_ring(struct intel_ring_buffer *ring)
+{
+	struct drm_i915_private *dev_priv = to_i915(ring->dev);
+
+	if (!IS_GEN2(ring->dev)) {
+		I915_WRITE_MODE(ring, _MASKED_BIT_ENABLE(STOP_RING));
+		if (wait_for_atomic((I915_READ_MODE(ring) & MODE_IDLE) != 0, 1000)) {
+			DRM_ERROR("%s :timed out trying to stop ring\n", ring->name);
+			return false;
+		}
+	}
+
+	I915_WRITE_CTL(ring, 0);
+	I915_WRITE_HEAD(ring, 0);
+	ring->write_tail(ring, 0);
+
+	if (!IS_GEN2(ring->dev)) {
+		(void)I915_READ_CTL(ring);
+		I915_WRITE_MODE(ring, _MASKED_BIT_DISABLE(STOP_RING));
+	}
+
+	return (I915_READ_HEAD(ring) & HEAD_ADDR) == 0;
+}
+
 static int init_ring_common(struct intel_ring_buffer *ring)
 {
 	struct drm_device *dev = ring->dev;
 	struct drm_i915_private *dev_priv = dev->dev_private;
 	struct drm_i915_gem_object *obj = ring->obj;
 	int ret = 0;
-	u32 head;
 
 	gen6_gt_force_wake_get(dev_priv, FORCEWAKE_ALL);
 
-	/* Stop the ring if it's running. */
-	I915_WRITE_CTL(ring, 0);
-	I915_WRITE_HEAD(ring, 0);
-	ring->write_tail(ring, 0);
-	if (wait_for_atomic((I915_READ_MODE(ring) & MODE_IDLE) != 0, 1000))
-		DRM_ERROR("%s :timed out trying to stop ring\n", ring->name);
-
-	if (I915_NEED_GFX_HWS(dev))
-		intel_ring_setup_status_page(ring);
-	else
-		ring_setup_phys_status_page(ring);
-
-	head = I915_READ_HEAD(ring) & HEAD_ADDR;
-
-	/* G45 ring initialization fails to reset head to zero */
-	if (head != 0) {
+	if (!stop_ring(ring)) {
+		/* G45 ring initialization often fails to reset head to zero */
 		DRM_DEBUG_KMS("%s head not reset to zero "
 			      "ctl %08x head %08x tail %08x start %08x\n",
 			      ring->name,
@@ -471,9 +480,7 @@ static int init_ring_common(struct intel_ring_buffer *ring)
 			      I915_READ_TAIL(ring),
 			      I915_READ_START(ring));
 
-		I915_WRITE_HEAD(ring, 0);
-
-		if (I915_READ_HEAD(ring) & HEAD_ADDR) {
+		if (!stop_ring(ring)) {
 			DRM_ERROR("failed to set %s head to zero "
 				  "ctl %08x head %08x tail %08x start %08x\n",
 				  ring->name,
@@ -481,9 +488,16 @@ static int init_ring_common(struct intel_ring_buffer *ring)
 				  I915_READ_HEAD(ring),
 				  I915_READ_TAIL(ring),
 				  I915_READ_START(ring));
+			ret = -EIO;
+			goto out;
 		}
 	}
 
+	if (I915_NEED_GFX_HWS(dev))
+		intel_ring_setup_status_page(ring);
+	else
+		ring_setup_phys_status_page(ring);
+
 	/* Initialize the ring. This must happen _after_ we've cleared the ring
 	 * registers with the above sequence (the readback of the HEAD registers
 	 * also enforces ordering), otherwise the hw might lose the new ring

drivers/gpu/drm/i915/intel_ringbuffer.h

@@ -34,6 +34,7 @@ struct  intel_hw_status_page {
 #define I915_WRITE_IMR(ring, val) I915_WRITE(RING_IMR((ring)->mmio_base), val)
 
 #define I915_READ_MODE(ring) I915_READ(RING_MI_MODE((ring)->mmio_base))
+#define I915_WRITE_MODE(ring, val) I915_WRITE(RING_MI_MODE((ring)->mmio_base), val)
 
 enum intel_ring_hangcheck_action {
 	HANGCHECK_IDLE = 0,