else
position = __raw_i915_read32(dev_priv, PIPEDSL(pipe)) & DSL_LINEMASK_GEN3;
+ /*
+ * On HSW, the DSL reg (0x70000) appears to return 0 if we
+ * read it just before the start of vblank. So try it again
+ * so we don't accidentally end up spanning a vblank frame
+ * increment, causing the pipe_update_end() code to squak at us.
+ *
+ * The nature of this problem means we can't simply check the ISR
+ * bit and return the vblank start value; nor can we use the scanline
+ * debug register in the transcoder as it appears to have the same
+ * problem. We may need to extend this to include other platforms,
+ * but so far testing only shows the problem on HSW.
+ */
+ if (IS_HASWELL(dev) && !position) {
+ int i, temp;
+
+ for (i = 0; i < 100; i++) {
+ udelay(1);
+ temp = __raw_i915_read32(dev_priv, PIPEDSL(pipe)) &
+ DSL_LINEMASK_GEN3;
+ if (temp != position) {
+ position = temp;
+ break;
+ }
+ }
+ }
+
/*
* See update_scanline_offset() for the details on the
* scanline_offset adjustment.