drm/i915: Mark FIFO underrun disabled earlier

At least on some platforms (tested on ctg) the way
vgacon does screen blanking seems to flag constant
FIFO underruns, which means we have to be prepared
for them while the driver is loading. Currently
there is a time window between drm_crtc_init() and
intel_sanitize_fifo_underrun_reporting() during
which FIFO underrun reporting is in fact marked as
enabled. Thus we may end up mistakenly detecting
these bogus underruns during driver init.

Close the race by marking FIFO underrun reporting
as disabled prior to even registering the crtc.
intel_sanitize_fifo_underrun_reporting()/etc. will
re-enable it later if needed.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230125185234.21599-2-ville.syrjala@linux.intel.com
Reviewed-by: Vinod Govindapillai <vinod.govindapillai@intel.com>

1 files changed, 20 insertions, 0 deletions

diff --git a/drivers/gpu/drm/i915/display/intel_fifo_underrun.c b/drivers/gpu/drm/i915/display/intel_fifo_underrun.c
index d636d21fa9ce..b708a62e509a 100644
--- a/drivers/gpu/drm/i915/display/intel_fifo_underrun.c
+++ b/drivers/gpu/drm/i915/display/intel_fifo_underrun.c
@@ -31,6 +31,7 @@
 #include "intel_display_types.h"
 #include "intel_fbc.h"
 #include "intel_fifo_underrun.h"
+#include "intel_pch_display.h"
 
 /**
  * DOC: fifo underrun handling
@@ -509,3 +510,22 @@ void intel_check_pch_fifo_underruns(struct drm_i915_private *dev_priv)
 
 	spin_unlock_irq(&dev_priv->irq_lock);
 }
+
+void intel_init_fifo_underrun_reporting(struct drm_i915_private *i915,
+					struct intel_crtc *crtc,
+					bool enable)
+{
+	crtc->cpu_fifo_underrun_disabled = !enable;
+
+	/*
+	 * We track the PCH trancoder underrun reporting state
+	 * within the crtc. With crtc for pipe A housing the underrun
+	 * reporting state for PCH transcoder A, crtc for pipe B housing
+	 * it for PCH transcoder B, etc. LPT-H has only PCH transcoder A,
+	 * and marking underrun reporting as disabled for the non-existing
+	 * PCH transcoders B and C would prevent enabling the south
+	 * error interrupt (see cpt_can_enable_serr_int()).
+	 */
+	if (intel_has_pch_trancoder(i915, crtc->pipe))
+		crtc->pch_fifo_underrun_disabled = !enable;
+}