drm/i915: Document which RING_FAULT bits apply to which platforms

The RING_FAULT bits have change a bit over the years. Document
which platforms use which bits.

Signed-off-by: Ville Syrjälä <[email protected]>
Reviewed-by: Andi Shyti <[email protected]>
Signed-off-by: Andi Shyti <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]

Author: vsyrjala

drivers/gpu/drm/i915/gt/intel_gt_regs.h

@@ -326,10 +326,10 @@
 							    _RING_FAULT_REG_VCS, \
 							    _RING_FAULT_REG_VECS, \
 							    _RING_FAULT_REG_BCS))
-#define   RING_FAULT_ENGINE_ID_MASK		REG_GENMASK(16, 12)
-#define   RING_FAULT_GTTSEL_MASK		REG_BIT(11)
+#define   RING_FAULT_ENGINE_ID_MASK		REG_GENMASK(16, 12) /* bdw+ */
+#define   RING_FAULT_GTTSEL_MASK		REG_BIT(11) /* pre-bdw */
 #define   RING_FAULT_SRCID_MASK			REG_GENMASK(10, 3)
-#define   RING_FAULT_FAULT_TYPE_MASK		REG_GENMASK(2, 1)
+#define   RING_FAULT_FAULT_TYPE_MASK		REG_GENMASK(2, 1) /* ivb+ */
 #define   RING_FAULT_VALID			REG_BIT(0)
 
 #define ERROR_GEN6				_MMIO(0x40a0)