[Intel-gfx] [PATCH] drm/i915: implement another plane WM workaround for HSW

Paulo Zanoni przanoni at gmail.com
Wed Sep 11 21:14:11 CEST 2013

From: Paulo Zanoni <paulo.r.zanoni at intel.com>

In some Haswell machines we're seeing a full system hang while calling
haswell_crtc_enable. Ville bisected the problem to the following
    commit 90a8864320b2a9f91e5b5d561924a4bb70b90dcc
    Author: Paulo Zanoni <paulo.r.zanoni at intel.com>
    Date:   Fri May 3 17:23:45 2013 -0300
        drm/i915: set FORCE_ARB_IDLE_PLANES workaround

After some BSpec-digging I discovered that we don't implement one of
the workarounds mentioned in the description of bit 31 of PRI_CTL,
SPR_CTL and CUR_CTL. This patch implements the workaround, which makes
the problem go away on my machine. Also notice that the workaround
implementation is almost a revert of the commit mentioned above, but
it still allows LP watermarks to be used.

Thanks to Ville for the help debugging the issue and for doing the

Cc: stable at vger.kernel.org
Credits-to: Ville Syrjälä <ville.syrjala at linux.intel.com>
Signed-off-by: Paulo Zanoni <paulo.r.zanoni at intel.com>
 drivers/gpu/drm/i915/intel_display.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 3c0e0cf..6e9c44a 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -3359,6 +3359,7 @@ static void haswell_crtc_enable(struct drm_crtc *crtc)
 	struct intel_encoder *encoder;
 	int pipe = intel_crtc->pipe;
 	int plane = intel_crtc->plane;
+	uint32_t wm_dbg_val;
@@ -3391,6 +3392,11 @@ static void haswell_crtc_enable(struct drm_crtc *crtc)
+	/* Workaround described in PRI_CTL, CUR_CTL and SPR_CTL bit 31. */
+	wm_dbg_val = I915_READ(WM_DBG);
 	intel_enable_pipe(dev_priv, pipe,
 			  intel_crtc->config.has_pch_encoder, false);
@@ -3421,6 +3427,9 @@ static void haswell_crtc_enable(struct drm_crtc *crtc)
 	 * happening.
 	intel_wait_for_vblank(dev, intel_crtc->pipe);
+	/* Second part of the WM_DBG workaround. */
+	I915_WRITE(WM_DBG, wm_dbg_val);
 static void ironlake_pfit_disable(struct intel_crtc *crtc)

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