drm/i915/bdw: Interrupts with logical rings

We need to attend context switch interrupts from all rings. Also, fixed writing
IMR/IER and added HWSTAM at ring init time.

Notice that, if added to irq_enable_mask, the context switch interrupts would
be incorrectly masked out when the user interrupts are due to no users waiting
on a sequence number. Therefore, this commit adds a bitmask of interrupts to
be kept unmasked at all times.

v2: Disable HWSTAM, as suggested by Damien (nobody listens to these interrupts,
anyway).

v3: Add new get/put_irq functions.

Signed-off-by: Thomas Daniel <thomas.daniel@intel.com> (v1)
Signed-off-by: Oscar Mateo <oscar.mateo@intel.com> (v2 & v3)
Reviewed-by: Damien Lespiau <damien.lespiau@intel.com>
[danvet: Drop the GEN8_ prefix from the context switch interrupt
define and move it to its brethren.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
index 36eb1f2..00957fa 100644
--- a/drivers/gpu/drm/i915/i915_irq.c
+++ b/drivers/gpu/drm/i915/i915_irq.c
@@ -1647,6 +1647,8 @@
 				notify_ring(dev, &dev_priv->ring[RCS]);
 			if (bcs & GT_RENDER_USER_INTERRUPT)
 				notify_ring(dev, &dev_priv->ring[BCS]);
+			if ((rcs | bcs) & GT_CONTEXT_SWITCH_INTERRUPT)
+				DRM_DEBUG_DRIVER("TODO: Context switch\n");
 		} else
 			DRM_ERROR("The master control interrupt lied (GT0)!\n");
 	}
@@ -1659,9 +1661,13 @@
 			vcs = tmp >> GEN8_VCS1_IRQ_SHIFT;
 			if (vcs & GT_RENDER_USER_INTERRUPT)
 				notify_ring(dev, &dev_priv->ring[VCS]);
+			if (vcs & GT_CONTEXT_SWITCH_INTERRUPT)
+				DRM_DEBUG_DRIVER("TODO: Context switch\n");
 			vcs = tmp >> GEN8_VCS2_IRQ_SHIFT;
 			if (vcs & GT_RENDER_USER_INTERRUPT)
 				notify_ring(dev, &dev_priv->ring[VCS2]);
+			if (vcs & GT_CONTEXT_SWITCH_INTERRUPT)
+				DRM_DEBUG_DRIVER("TODO: Context switch\n");
 		} else
 			DRM_ERROR("The master control interrupt lied (GT1)!\n");
 	}
@@ -1685,6 +1691,8 @@
 			vcs = tmp >> GEN8_VECS_IRQ_SHIFT;
 			if (vcs & GT_RENDER_USER_INTERRUPT)
 				notify_ring(dev, &dev_priv->ring[VECS]);
+			if (vcs & GT_CONTEXT_SWITCH_INTERRUPT)
+				DRM_DEBUG_DRIVER("TODO: Context switch\n");
 		} else
 			DRM_ERROR("The master control interrupt lied (GT3)!\n");
 	}
@@ -3788,12 +3796,17 @@
 	/* These are interrupts we'll toggle with the ring mask register */
 	uint32_t gt_interrupts[] = {
 		GT_RENDER_USER_INTERRUPT << GEN8_RCS_IRQ_SHIFT |
+			GT_CONTEXT_SWITCH_INTERRUPT << GEN8_RCS_IRQ_SHIFT |
 			GT_RENDER_L3_PARITY_ERROR_INTERRUPT |
-			GT_RENDER_USER_INTERRUPT << GEN8_BCS_IRQ_SHIFT,
+			GT_RENDER_USER_INTERRUPT << GEN8_BCS_IRQ_SHIFT |
+			GT_CONTEXT_SWITCH_INTERRUPT << GEN8_BCS_IRQ_SHIFT,
 		GT_RENDER_USER_INTERRUPT << GEN8_VCS1_IRQ_SHIFT |
-			GT_RENDER_USER_INTERRUPT << GEN8_VCS2_IRQ_SHIFT,
+			GT_CONTEXT_SWITCH_INTERRUPT << GEN8_VCS1_IRQ_SHIFT |
+			GT_RENDER_USER_INTERRUPT << GEN8_VCS2_IRQ_SHIFT |
+			GT_CONTEXT_SWITCH_INTERRUPT << GEN8_VCS2_IRQ_SHIFT,
 		0,
-		GT_RENDER_USER_INTERRUPT << GEN8_VECS_IRQ_SHIFT
+		GT_RENDER_USER_INTERRUPT << GEN8_VECS_IRQ_SHIFT |
+			GT_CONTEXT_SWITCH_INTERRUPT << GEN8_VECS_IRQ_SHIFT
 		};
 
 	for (i = 0; i < ARRAY_SIZE(gt_interrupts); i++)