drm/i915: rename INSTDONE1 to GEN4_INSTDONE1

This register was added on GEN4, by the name INSTDONE_1 whereas the GEN6
specification calls it INSTDONE_2. Keep the original name with a
platform prefix to make it clearer which INSTDONE register instance this
is. Also add a comment about the SNB alternative name.
Signed-off-by: NImre Deak <imre.deak@intel.com>
Reviewed-by: NBen Widawsky <ben@bwidawsk.net>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_gpu_error.c

@@ -1391,7 +1391,7 @@ void i915_get_extra_instdone(struct drm_device *dev, uint32_t *instdone)
 		instdone[0] = I915_READ(GEN2_INSTDONE);
 	else if (IS_GEN4(dev) || IS_GEN5(dev) || IS_GEN6(dev)) {
 		instdone[0] = I915_READ(RING_INSTDONE(RENDER_RING_BASE));
-		instdone[1] = I915_READ(INSTDONE1);
+		instdone[1] = I915_READ(GEN4_INSTDONE1);
 	} else if (INTEL_INFO(dev)->gen >= 7) {
 		instdone[0] = I915_READ(RING_INSTDONE(RENDER_RING_BASE));
 		instdone[1] = I915_READ(GEN7_SC_INSTDONE);

drivers/gpu/drm/i915/i915_reg.h

@@ -1611,7 +1611,7 @@ enum skl_disp_power_wells {
 #define RING_INSTPM(base)	((base)+0xc0)
 #define RING_MI_MODE(base)	((base)+0x9c)
 #define INSTPS		0x02070 /* 965+ only */
-#define INSTDONE1	0x0207c /* 965+ only */
+#define GEN4_INSTDONE1	0x0207c /* 965+ only, aka INSTDONE_2 on SNB */
 #define ACTHD_I965	0x02074
 #define HWS_PGA		0x02080
 #define HWS_ADDRESS_MASK	0xfffff000