[PATCH 5/5] drm/i915/cx0: Read out power-down state of both PHY lanes for reversed lanes

[Imre Deak <imre.deak@intel.com>]

For a port used with lane reversal enabled the first two TX lanes will
be enabled in PHY lane#1 instead of PHY lane#0. At the moment the HW
readout will read out the power-down state for these two TX lanes from
PHY lane#0 incorrectly. The display HW lane reversal feature (vs. the
similar TCSS lane swap) is only used for TypeC legacy mode and for
non-TypeC PHYs. Since in both of these cases the display owns both PHY
lanes, both of these PHY lanes' state can be read out. Do that to fix
cases when lane reversal is used with 1 or 2 active TX lanes.

While at it add an assert to the PLL enable function about the above
assumption on when lane reversal can be used.

Cc: Mika Kahola <mika.kahola@intel.com>
Cc: Suraj Kandpal <suraj.kandpal@intel.com>
Fixes: 230d4c748113 ("drm/i915/cx0: Track the Cx0 PHY enabled lane count in the PLL state")
Signed-off-by: Imre Deak <imre.deak@intel.com>
---
 drivers/gpu/drm/i915/display/intel_cx0_phy.c | 24 ++++++++++++++++++--
 1 file changed, 22 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_cx0_phy.c b/drivers/gpu/drm/i915/display/intel_cx0_phy.c
index 0d524735dcf95..27be2a490297f 100644
--- a/drivers/gpu/drm/i915/display/intel_cx0_phy.c
+++ b/drivers/gpu/drm/i915/display/intel_cx0_phy.c
@@ -2197,17 +2197,30 @@ static int readout_enabled_lane_count(struct intel_encoder *encoder)
 {
 	struct intel_display *display = to_intel_display(encoder);
 	u8 enabled_tx_lane_count = 0;
-	int max_tx_lane_count;
+	int max_tx_lane_count = 4;
+	bool lane_reversal;
 	int tx_lane;
 
+	lane_reversal = intel_de_read(display, XELPDP_PORT_BUF_CTL1(display, encoder->port)) &
+			XELPDP_PORT_REVERSAL;
+
 	/*
 	 * TODO: also check inactive TX lanes in all PHY lanes owned by the
 	 * display. For now checking only those PHY lane(s) which are owned
 	 * based on the active TX lane count (i.e.
 	 *   1,2 active TX lanes -> PHY lane#0
 	 *   3,4 active TX lanes -> PHY lane#0 and PHY lane#1).
+	 *
+	 * In case of lane reversal for 1, 2 active TX lanes, only PHY
+	 * lane#1 is used. This is only possible in TypeC legacy mode or if
+	 * the port is connected to a non-TC PHY. In both of these cases both
+	 * PHY lane#0 and #1 are owned by display, so check all 4 TX lanes in
+	 * both PHY lanes in those cases.
 	 */
-	max_tx_lane_count = DDI_PORT_WIDTH_GET(intel_de_read(display, DDI_BUF_CTL(encoder->port)));
+	if (!lane_reversal)
+		max_tx_lane_count = DDI_PORT_WIDTH_GET(intel_de_read(display,
+								     DDI_BUF_CTL(encoder->port)));
+
 	if (!drm_WARN_ON(display->drm, max_tx_lane_count == 0))
 		max_tx_lane_count = round_up(max_tx_lane_count, 2);
 
@@ -3214,6 +3227,13 @@ static void intel_cx0pll_enable(struct intel_encoder *encoder,
 					  INTEL_CX0_LANE0;
 	intel_wakeref_t wakeref = intel_cx0_phy_transaction_begin(encoder);
 
+	/*
+	 * Lane reversal is never used in DP-alt mode, in that case the
+	 * corresponding lane swapping (based on the TypeC cable flip state
+	 * for instance) is handled automatically by the HW via a TCSS mux.
+	 */
+	drm_WARN_ON(display->drm, lane_reversal && intel_tc_port_in_dp_alt_mode(dig_port));
+
 	/*
 	 * 1. Program PORT_CLOCK_CTL REGISTER to configure
 	 * clock muxes, gating and SSC
-- 
2.49.1