[Intel-gfx] [PATCH 2/2] drm/i915: Ignore stale wm register values on resume on ilk-bdw

[ville.syrjala at linux.intel.com]

From: Ville Syrjälä <ville.syrjala at linux.intel.com>

When we resume the watermark register may contain some BIOS leftovers,
or just the hardware reset values. We should ignore those as the
pipes will be off anyway, and so frobbing around with intermediate
watermarks doesn't make much sense.

In fact I think we should just throw the skip_intermediate_wm flag
out, and instead properly sanitize the "active" watermarks to match
the current plane and pipe states. The actual wm state readout might
also need a bit of work. But for now, let's continue with the
skip_intermediate_wm to keep the fix more minimal.

Fixes this sort of errors on resume
[drm:ilk_validate_pipe_wm] LP0 watermark invalid
[drm:intel_crtc_atomic_check] No valid intermediate pipe watermarks are possible
[drm:intel_display_resume [i915]] *ERROR* Restoring old state failed with -22
and a boatload of subsequent modeset BAT fails on my ILK.

Cc: Matt Roper <matthew.d.roper at intel.com>
Cc: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
Fixes: ed4a6a7ca853 ("drm/i915: Add two-stage ILK-style watermark programming (v11)")
Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
---
 drivers/gpu/drm/i915/intel_display.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index a08c4a45b8d3..938653063f15 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -12003,6 +12003,9 @@ static int intel_crtc_atomic_check(struct drm_crtc *crtc,
 			DRM_DEBUG_KMS("No valid intermediate pipe watermarks are possible\n");
 			return ret;
 		}
+	} else if (dev_priv->display.compute_intermediate_wm) {
+		if (HAS_PCH_SPLIT(dev_priv) && INTEL_GEN(dev_priv) < 9)
+			pipe_config->wm.intermediate = pipe_config->wm.optimal.ilk;
 	}
 
 	if (INTEL_INFO(dev)->gen >= 9) {
@@ -15991,6 +15994,9 @@ retry:
 
 		state->acquire_ctx = &ctx;
 
+		/* ignore any reset values/BIOS leftovers in the WM registers */
+		to_intel_atomic_state(state)->skip_intermediate_wm = true;
+
 		for_each_crtc_in_state(state, crtc, crtc_state, i) {
 			/*
 			 * Force recalculation even if we restore
-- 
2.7.4