[PATCH 1/3] drm/i915/cx0: check PLL ACK bit in intel_cx0_pll_is_enabled()

[Aaron Esau <aaron1esau@gmail.com>]

intel_cx0_pll_is_enabled() only checks the PCLK_PLL_REQUEST bit in
PORT_CLOCK_CTL, which is set by the driver during the PLL enable
sequence. It does not check the PCLK_PLL_ACK bit, which is the
hardware's response indicating the PLL actually locked.

When the CX0 PHY MSGBUS is unresponsive (e.g. after a failed s2idle
resume), the PLL register programming via MSGBUS silently fails and
the PLL never locks, but intel_cx0_pll_is_enabled() returns true
because the driver-set REQUEST bit is present. This causes all
downstream state readout and verification to operate on a PLL that
is not actually enabled.

Check both the REQUEST and ACK bits so that a PLL is only reported
as enabled when the hardware has confirmed it locked.

Fixes: bf8531990380 ("drm/i915/display: Allow display PHYs to reset power state")
Cc: stable@vger.kernel.org
Cc: Mika Kahola <mika.kahola@intel.com>
Signed-off-by: Aaron Esau <aaron1esau@gmail.com>
---
 drivers/gpu/drm/i915/display/intel_cx0_phy.c | 7 +++++--
 1 file changed, 5 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 7288065d2..4cacea802 100644
--- a/drivers/gpu/drm/i915/display/intel_cx0_phy.c
+++ b/drivers/gpu/drm/i915/display/intel_cx0_phy.c
@@ -3581,9 +3581,12 @@ 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;
+	u32 val;
 
-	return intel_de_read(display, XELPDP_PORT_CLOCK_CTL(display, encoder->port)) &
-			     intel_cx0_get_pclk_pll_request(lane);
+	val = intel_de_read(display, XELPDP_PORT_CLOCK_CTL(display, encoder->port));
+
+	return (val & intel_cx0_get_pclk_pll_request(lane)) &&
+	       (val & intel_cx0_get_pclk_pll_ack(lane));
 }
 
 void intel_mtl_tbt_pll_disable_clock(struct intel_encoder *encoder)
-- 
2.54.0