drm/i915/dsi: fix bxt split screen and color issue

Fix the failure mode where the display appears split, or shifted about
2/3 of the screen, and the color components are cycled. Turns out we
were missing the crucial BXT_DEFEATURE_DPI_FIFO_CTR bit in the
EOT_DISABLE register.

Per bspec, with the bit set, the "mipi_dpf_vblank_start" signal is
asserted only when the complete frame is transferred in the DPHY line
and also the DPI FIFO is flushed out at the end of each frame.

The problem was mitigated by keeping the panel fitter enabled, but that
only limited the issue to a shift of about 0..10 pixels. With the fix
here, the panel fitter workaround does not seem to be needed at all.

While at it, set BXT_DPHY_DEFEATURE_EN in EOT_DISABLE register which is
also needed per the BXT DSI mode set sequence.

Issue: VIZ-7610
Cc: Mika Kahola <mika.kahola@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Ramalingam C <ramalingam.c@intel.com>
Cc: Uma Shankar <uma.shankar@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1464965825-31035-1-git-send-email-jani.nikula@intel.com

drivers/gpu/drm/i915/i915_reg.h

@@ -8151,6 +8151,8 @@ enum skl_disp_power_wells {
 #define _MIPIA_EOT_DISABLE		(dev_priv->mipi_mmio_base + 0xb05c)
 #define _MIPIC_EOT_DISABLE		(dev_priv->mipi_mmio_base + 0xb85c)
 #define MIPI_EOT_DISABLE(port)		_MMIO_MIPI(port, _MIPIA_EOT_DISABLE, _MIPIC_EOT_DISABLE)
+#define  BXT_DEFEATURE_DPI_FIFO_CTR			(1 << 9)
+#define  BXT_DPHY_DEFEATURE_EN				(1 << 8)
 #define  LP_RX_TIMEOUT_ERROR_RECOVERY_DISABLE		(1 << 7)
 #define  HS_RX_TIMEOUT_ERROR_RECOVERY_DISABLE		(1 << 6)
 #define  LOW_CONTENTION_RECOVERY_DISABLE		(1 << 5)

drivers/gpu/drm/i915/intel_dsi.c

@@ -1172,6 +1172,12 @@ static void intel_dsi_prepare(struct intel_encoder *intel_encoder)
 	if (intel_dsi->clock_stop)
 		tmp |= CLOCKSTOP;
 
+	if (IS_BROXTON(dev_priv)) {
+		tmp |= BXT_DPHY_DEFEATURE_EN;
+		if (!is_cmd_mode(intel_dsi))
+			tmp |= BXT_DEFEATURE_DPI_FIFO_CTR;
+	}
+
 	for_each_dsi_port(port, intel_dsi->ports) {
 		I915_WRITE(MIPI_DSI_FUNC_PRG(port), val);