drm/i915/display: Write PHY_CMN1_CONTROL only when using AUXLess ALPM

We are seeing "dmesg-warn/abort - *ERROR* PHY * failed after 3 retries"
since we started configuring LFPS sending. According to Bspec Configuring
LFPS sending is needed only when using AUXLess ALPM. This patch avoids
these failures by configuring LFPS sending only when using AUXLess ALPM.

Bspec: 68849
Fixes: 9dc6196 ("drm/i915/display: Add function to configure LFPS sending")
Signed-off-by: Jouni Högander <jouni.hogander@intel.com>
Reviewed-by: Gustavo Sousa <gustavo.sousa@intel.com>
Link: https://lore.kernel.org/r/20250722125618.1842615-2-jouni.hogander@intel.com
(cherry picked from commit 8265ce0)
Signed-off-by: Tvrtko Ursulin <tursulin@ursulin.net>

Author: hogander

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

@@ -3240,11 +3240,10 @@ void intel_lnl_mac_transmit_lfps(struct intel_encoder *encoder,
 {
 	struct intel_display *display = to_intel_display(encoder);
 	u8 owned_lane_mask = intel_cx0_get_owned_lane_mask(encoder);
-	bool enable = intel_alpm_is_alpm_aux_less(enc_to_intel_dp(encoder),
-						  crtc_state);
 	int i;
 
-	if (DISPLAY_VER(display) < 20)
+	if (DISPLAY_VER(display) < 20 ||
+	    !intel_alpm_is_alpm_aux_less(enc_to_intel_dp(encoder), crtc_state))
 		return;
 
 	for (i = 0; i < 4; i++) {
@@ -3256,8 +3255,7 @@ void intel_lnl_mac_transmit_lfps(struct intel_encoder *encoder,
 
 		intel_cx0_rmw(encoder, lane_mask, PHY_CMN1_CONTROL(tx, 0),
 			      CONTROL0_MAC_TRANSMIT_LFPS,
-			      enable ? CONTROL0_MAC_TRANSMIT_LFPS : 0,
-			      MB_WRITE_COMMITTED);
+			      CONTROL0_MAC_TRANSMIT_LFPS, MB_WRITE_COMMITTED);
 	}
 }