drm/i915: set the LPT FDI RX polarity reversal bit when needed
If we fail to set the bit when needed we get some nice FDI link
training failures (AKA "black screen on VGA output").
While we don't really know how to properly choose whether we need to
set the bit or not (VBT?), just read the initial value set by the BIOS
and store it for later usage.
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/intel_crt.c b/drivers/gpu/drm/i915/intel_crt.c
index 3084d01..fe20bf7 100644
--- a/drivers/gpu/drm/i915/intel_crt.c
+++ b/drivers/gpu/drm/i915/intel_crt.c
@@ -798,4 +798,12 @@
crt->force_hotplug_required = 0;
dev_priv->hotplug_supported_mask |= CRT_HOTPLUG_INT_STATUS;
+
+ /*
+ * TODO: find a proper way to discover whether we need to set the
+ * polarity reversal bit or not, instead of relying on the BIOS.
+ */
+ if (HAS_PCH_LPT(dev))
+ dev_priv->fdi_rx_polarity_reversed =
+ !!(I915_READ(_FDI_RXA_CTL) & FDI_RX_POLARITY_REVERSED_LPT);
}