drm/i915: workaround bad DSL readout v3 (41b578fb) · Commits · e / devices / android_kernel_teracube_emerald

On HSW at least (still testing other platforms, but should be harmless elsewhere), the DSL reg reads back as 0 when read around vblank start time. This ends up confusing the atomic start/end checking code, since it causes the update to appear as if it crossed a frame count boundary. Avoid the problem by making sure we don't return scanline_offset from the get_crtc_scanline function. In moving the code there, I add to add an additional delay since it could be called and have a legitimate 0 result for some time (depending on the pixel clock). v2: move hsw dsl read hack to get_crtc_scanline (Ville) v3: use break instead of goto (Ville) update comment with workaround details (Ville) References: https://bugs.freedesktop.org/show_bug.cgi?id=91579 Signed-off-by:

Jesse Barnes <jbarnes@virtuousgeek.org> Reviewed-by:

Ville Syrjälä <ville.syrjala@linux.intel.com> Signed-off-by:

Jani Nikula <jani.nikula@intel.com>

drivers/gpu/drm/i915/i915_irq.c

+26 −0

Original line number	Diff line number	Diff line
		@@ -639,6 +639,32 @@ static int __intel_get_crtc_scanline(struct intel_crtc *crtc)
		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.