drm/i915: Fix gen4 GPU reset

On pre-ctg the reset bit directly controls the reset signal. We must
assert it for >=20usec and then deassert it. Bit 1 is a RO status bit
which should also go down when the reset is no longer asserted.

Tested-by: Kenneth Graunke <kenneth@whitecape.org>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_reg.h

@@ -83,6 +83,7 @@
 #define  GRDOM_RENDER	(1<<2)
 #define  GRDOM_MEDIA	(3<<2)
 #define  GRDOM_MASK	(3<<2)
+#define  GRDOM_RESET_STATUS (1<<1)
 #define  GRDOM_RESET_ENABLE (1<<0)
 
 #define ILK_GDSR 0x2ca4 /* MCHBAR offset */

drivers/gpu/drm/i915/intel_uncore.c

@@ -1349,37 +1349,24 @@ static int i965_reset_complete(struct drm_device *dev)
 {
 	u8 gdrst;
 	pci_read_config_byte(dev->pdev, I965_GDRST, &gdrst);
-	return (gdrst & GRDOM_RESET_ENABLE) == 0;
+	return (gdrst & GRDOM_RESET_STATUS) == 0;
 }
 
 static int i965_do_reset(struct drm_device *dev)
 {
-	int ret;
-
-	/* FIXME: i965g/gm need a display save/restore for gpu reset. */
-	return -ENODEV;
-
-	/*
-	 * Set the domains we want to reset (GRDOM/bits 2 and 3) as
-	 * well as the reset bit (GR/bit 0).  Setting the GR bit
-	 * triggers the reset; when done, the hardware will clear it.
-	 */
-	pci_write_config_byte(dev->pdev, I965_GDRST,
-			      GRDOM_RENDER | GRDOM_RESET_ENABLE);
-	ret =  wait_for(i965_reset_complete(dev), 500);
-	if (ret)
-		return ret;
-
-	pci_write_config_byte(dev->pdev, I965_GDRST,
-			      GRDOM_MEDIA | GRDOM_RESET_ENABLE);
-
-	ret =  wait_for(i965_reset_complete(dev), 500);
-	if (ret)
-		return ret;
-
+	/* assert reset for at least 20 usec */
+	pci_write_config_byte(dev->pdev, I965_GDRST, GRDOM_RESET_ENABLE);
+	udelay(20);
 	pci_write_config_byte(dev->pdev, I965_GDRST, 0);
 
-	return 0;
+	return wait_for(i965_reset_complete(dev), 500);
+}
+
+static int g4x_reset_complete(struct drm_device *dev)
+{
+	u8 gdrst;
+	pci_read_config_byte(dev->pdev, I965_GDRST, &gdrst);
+	return (gdrst & GRDOM_RESET_ENABLE) == 0;
 }
 
 static int g4x_do_reset(struct drm_device *dev)
@@ -1389,7 +1376,7 @@ static int g4x_do_reset(struct drm_device *dev)
 
 	pci_write_config_byte(dev->pdev, I965_GDRST,
 			      GRDOM_RENDER | GRDOM_RESET_ENABLE);
-	ret =  wait_for(i965_reset_complete(dev), 500);
+	ret =  wait_for(g4x_reset_complete(dev), 500);
 	if (ret)
 		return ret;
 
@@ -1399,7 +1386,7 @@ static int g4x_do_reset(struct drm_device *dev)
 
 	pci_write_config_byte(dev->pdev, I965_GDRST,
 			      GRDOM_MEDIA | GRDOM_RESET_ENABLE);
-	ret =  wait_for(i965_reset_complete(dev), 500);
+	ret =  wait_for(g4x_reset_complete(dev), 500);
 	if (ret)
 		return ret;