drm/i915/display: Allow display PHYs to reset power state

The dedicated display PHYs reset to a power state that blocks S0ix,
increasing idle system power. After a system reset (cold boot,
S3/4/5, warm reset) if a dedicated PHY is not being brought up
shortly, use these steps to move the PHY to the lowest power state
to save power.

1. Follow the PLL Enable Sequence, using any valid frequency such
   as DP 1.62 GHz. This brings lanes out of reset and enables the
   PLL to allow powerdown to be moved to the Disable state.
2. Follow PLL Disable Sequence. This moves powerdown to the Disable
   state and disables the PLL.

v2: Rename WA function to more descriptive (Jani)
    For PTL, only port A needs this wa
    Add helpers to check presence of C10 phy and pll enabling (Imre)
v3: Rename wa function (Imre)
    Check return value of C10 pll tables readout (Imre)
    Use PLL request to check pll enabling (Imre)
v4: Move intel_cx0_pll_is_enabled() right after
    intel_cx0_pll_disable() (Imre)
    Add drm_WARN_ON() if C10 state cannot be calculated from
    the tables (Imre)
v5: Add debug message on PLL enabling (Imre)
    Add check for intel_encoder_is_dig_port() (Imre)

Signed-off-by: Mika Kahola <mika.kahola@intel.com>
Reviewed-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250218100019.740556-3-mika.kahola@intel.com

Author: mkahola

drivers/gpu/drm/i915/display/intel_cx0_phy.c

@@ -3294,6 +3294,16 @@ static void intel_cx0pll_disable(struct intel_encoder *encoder)
 	intel_cx0_phy_transaction_end(encoder, wakeref);
 }
 
+static bool intel_cx0_pll_is_enabled(struct intel_encoder *encoder)
+{
+	struct intel_display *display = to_intel_display(encoder);
+	struct intel_digital_port *dig_port = enc_to_dig_port(encoder);
+	u8 lane = dig_port->lane_reversal ? INTEL_CX0_LANE1 : INTEL_CX0_LANE0;
+
+	return intel_de_read(display, XELPDP_PORT_CLOCK_CTL(display, encoder->port)) &
+			     intel_cx0_get_pclk_pll_request(lane);
+}
+
 static void intel_mtl_tbt_pll_disable(struct intel_encoder *encoder)
 {
 	struct intel_display *display = to_intel_display(encoder);
@@ -3555,3 +3565,54 @@ void intel_cx0pll_state_verify(struct intel_atomic_state *state,
 	else
 		intel_c20pll_state_verify(new_crtc_state, crtc, encoder, &mpll_hw_state.c20);
 }
+
+/*
+ * WA 14022081154
+ * The dedicated display PHYs reset to a power state that blocks S0ix, increasing idle
+ * system power. After a system reset (cold boot, S3/4/5, warm reset) if a dedicated
+ * PHY is not being brought up shortly, use these steps to move the PHY to the lowest
+ * power state to save power. For PTL the workaround is needed only for port A. Port B
+ * is not connected.
+ *
+ * 1. Follow the PLL Enable Sequence, using any valid frequency such as DP 1.62 GHz.
+ *    This brings lanes out of reset and enables the PLL to allow powerdown to be moved
+ *    to the Disable state.
+ * 2. Follow PLL Disable Sequence. This moves powerdown to the Disable state and disables the PLL.
+ */
+void intel_cx0_pll_power_save_wa(struct intel_display *display)
+{
+	struct intel_encoder *encoder;
+
+	if (DISPLAY_VER(display) != 30)
+		return;
+
+	for_each_intel_encoder(display->drm, encoder) {
+		struct intel_cx0pll_state pll_state = {};
+		int port_clock = 162000;
+
+		if (!intel_encoder_is_dig_port(encoder))
+			continue;
+
+		if (!intel_encoder_is_c10phy(encoder))
+			continue;
+
+		if (intel_cx0_pll_is_enabled(encoder))
+			continue;
+
+		if (intel_c10pll_calc_state_from_table(encoder,
+						       mtl_c10_edp_tables,
+						       true, port_clock,
+						       &pll_state) < 0) {
+			drm_WARN_ON(display->drm,
+				    "Unable to calc C10 state from the tables\n");
+			continue;
+		}
+
+		drm_dbg_kms(display->drm,
+			    "[ENCODER:%d:%s] Applying power saving workaround on disabled PLL\n",
+			    encoder->base.base.id, encoder->base.name);
+
+		__intel_cx0pll_enable(encoder, &pll_state, true, port_clock, 4);
+		intel_cx0pll_disable(encoder);
+	}
+}

drivers/gpu/drm/i915/display/intel_cx0_phy.h

@@ -42,5 +42,6 @@ bool intel_cx0pll_compare_hw_state(const struct intel_cx0pll_state *a,
 void intel_cx0_phy_set_signal_levels(struct intel_encoder *encoder,
 				     const struct intel_crtc_state *crtc_state);
 int intel_mtl_tbt_calc_port_clock(struct intel_encoder *encoder);
+void intel_cx0_pll_power_save_wa(struct intel_display *display);
 
 #endif /* __INTEL_CX0_PHY_H__ */

drivers/gpu/drm/i915/display/intel_display_reset.c

@@ -7,6 +7,7 @@
 
 #include "i915_drv.h"
 #include "intel_clock_gating.h"
+#include "intel_cx0_phy.h"
 #include "intel_display_driver.h"
 #include "intel_display_reset.h"
 #include "intel_display_types.h"
@@ -116,6 +117,7 @@ void intel_display_reset_finish(struct drm_i915_private *i915)
 		intel_pps_unlock_regs_wa(display);
 		intel_display_driver_init_hw(display);
 		intel_clock_gating_init(i915);
+		intel_cx0_pll_power_save_wa(display);
 		intel_hpd_init(i915);
 
 		ret = __intel_display_driver_resume(display, state, ctx);

drivers/gpu/drm/i915/display/intel_dpll_mgr.c

@@ -27,6 +27,7 @@
 #include "bxt_dpio_phy_regs.h"
 #include "i915_drv.h"
 #include "i915_reg.h"
+#include "intel_cx0_phy.h"
 #include "intel_de.h"
 #include "intel_display_types.h"
 #include "intel_dkl_phy.h"
@@ -4571,6 +4572,8 @@ void intel_dpll_sanitize_state(struct intel_display *display)
 	struct intel_shared_dpll *pll;
 	int i;
 
+	intel_cx0_pll_power_save_wa(display);
+
 	for_each_shared_dpll(display, pll, i)
 		sanitize_dpll_state(display, pll);
 }