drm/i915: Preserve the FDI line reversal override bit on CPT
The FDI link has supported link reversal to make the PCB layout
engineer's life easier for quite a while and we have always presered
this bit as we programmed FDI_RX_CTL with a read/modify/write sequence.
We're trying to take a bit more control over what the BIOS leaves in
various register and with the introduction of DDI, started to program
FDI_RX_CTL fully.
There's a fused bit to indicate DMI link reversal and FDI defaults to
mirroring that configuration. We have a bit to override that behaviour
that we need to preserve from the BIOS.
Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@gmail.com>
Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Cc: stable@vger.kernel.org
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 68e79f3..cfc9687 100644
--- a/drivers/gpu/drm/i915/intel_crt.c
+++ b/drivers/gpu/drm/i915/intel_crt.c
@@ -801,10 +801,14 @@
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.
+ * TODO: find a proper way to discover whether we need to set the the
+ * polarity and link reversal bits 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);
+ if (HAS_PCH_LPT(dev)) {
+ u32 fdi_config = FDI_RX_POLARITY_REVERSED_LPT |
+ FDI_RX_LINK_REVERSAL_OVERRIDE;
+
+ dev_priv->fdi_rx_config = I915_READ(_FDI_RXA_CTL) & fdi_config;
+ }
}