Step 11: Replace full init_settings with targeted pipe 3 setup

max9295_init_settings() writes to global serializer registers (0x02 pipe
enable, 0x308 CSI port select, 0x311 data source, 0x331 MIPI RX) that
disrupt the active GMSL link.  When called in Step 11  where the link
is UP (either naturally recovered or restored by Phase 1/2)  these
global register writes kill the link within ~34ms, cascading into total
I2C failure (-121) for all addresses (9-001a/b/c/d).

Replace with ds5_setup_pipeline() for pipe 3 (IMU) only.  This calls
max9295_set_pipe() + dser set_pipe() which write ONLY per-pipe registers
(data type, vc_id, BPP, LIM_HEART)  no global registers are touched
and the GMSL link remains stable.

The D457 FW configures pipes 0-2 (Depth, RGB, IR) during boot.
Pipe 3 (IMU) is the only one the driver must add post-reset.

Symptom: After HW reset via HWMC (light path), init_settings at T+236ms
kills the GMSL link.  34ms later all I2C addresses return -121, leading
to IMU stream start failure and eventually Phase 2 deserializer reset.

Author: sareluzi

kernel/realsense/d4xx.c

@@ -3103,53 +3103,50 @@ static int ds5_hw_reset_with_recovery(struct ds5 *state)
 		}
 	} /* if (serdes_recovery_ran) */
 
-	/* 11. Final SERDES pipe restoration (unconditional).
-	 *     The D457 FW continues reconfiguring the MAX9295 serializer
-	 *     for ~50-100ms after reporting 0xDEAD.  Any earlier call to
-	 *     max9295_init_settings() — whether from Phase 1 (heavy path)
-	 *     or skipped entirely (light path) — may have been overwritten
-	 *     by the FW's late-boot serializer init.  Re-applying the
-	 *     driver's authoritative pipe configuration here, after Steps
-	 *     7-10 have consumed enough time, ensures all 4 pipes —
-	 *     including pipe 3 (IMU, vc_id=3) — are correctly configured.
+	/* 11. Targeted pipe 3 (IMU) restoration (unconditional).
+	 *     The D457 FW configures MAX9295 pipes 0-2 (Depth, RGB, IR)
+	 *     during boot but does NOT configure pipe 3 (IMU, vc_id=3).
+	 *     Without pipe 3, the serializer has no I2C address translation
+	 *     for 9-001d and the IMU is unreachable (-EREMOTEIO / -121).
 	 *
-	 *     Light path: FW finished ~100ms after 0xDEAD but Steps 7-9
-	 *       may be as short as 12ms → need 150ms extra wait.
-	 *     Heavy path (Phase 1): Phase 1 itself takes ~750ms (100ms
-	 *       post-init sleep + 3×200ms stability reads) plus Steps 7-9,
-	 *       so the FW is long done → no extra wait needed.
-	 *     Heavy path (Phase 2): Full deser reset already called
-	 *       init_settings inside recovery, but re-calling is harmless
-	 *       insurance and keeps the logic simple.
+	 *     CRITICAL: Do NOT call max9295_init_settings() here.  That
+	 *     function writes to global registers (0x02 pipe enable, 0x308
+	 *     CSI port select, 0x311 pipe data source, 0x331 MIPI RX) that
+	 *     disrupt the active GMSL link.  The link is UP at this point
+	 *     (either naturally recovered or restored by Phase 1/2), and
+	 *     writing those global registers kills it immediately.
+	 *
+	 *     Instead, call ds5_setup_pipeline() for pipe 3 only.  This
+	 *     calls max9295_set_pipe() + dser set_pipe() which write ONLY
+	 *     per-pipe registers (data type, vc_id, BPP, LIM_HEART) —
+	 *     no global registers, no link disruption.
+	 *
+	 *     Light path: 150ms delay for FW to finish MAX9295 reconfig.
+	 *     Heavy path (Phase 1/2): no delay — FW is long done.
 	 */
 	{
-		int ser_ret, dser_ret;
+		int pipe3_ret;
 
 		if (!serdes_recovery_ran) {
-			/* Light path: FW may still be reconfiguring MAX9295.
-			 * Wait for it to finish before we overwrite its config.
+			/* Light path: FW continues writing to MAX9295 for
+			 * ~50-100ms after 0xDEAD.  Wait for it to finish
+			 * before we configure pipe 3.
 			 */
 			msleep(150);
 		}
-		/* Heavy path: no extra delay — Phase 1/2 already consumed
-		 * enough time for FW to finish MAX9295 reconfig.
-		 */
 
-		ser_ret = max9295_init_settings(state->ser_dev);
-		if (ser_ret)
+		pipe3_ret = ds5_setup_pipeline(state,
+					       GMSL_CSI_DT_YUV422_8,
+					       GMSL_CSI_DT_EMBED,
+					       3, /* pipe_id = 3 (IMU) */
+					       3  /* vc_id = 3 */);
+		if (pipe3_ret)
 			dev_warn(&state->client->dev,
-				"%s(): post-reset ser init_settings failed: %d\n",
-				__func__, ser_ret);
-
-		dser_ret = state->dser_ops->init_settings(state->dser_dev);
-		if (dser_ret)
-			dev_warn(&state->client->dev,
-				"%s(): post-reset deser init_settings failed: %d\n",
-				__func__, dser_ret);
-
-		if (!ser_ret && !dser_ret)
+				"%s(): post-reset pipe 3 (IMU) setup failed: %d\n",
+				__func__, pipe3_ret);
+		else
 			dev_info(&state->client->dev,
-				"%s(): SERDES pipe configuration restored after %s recovery\n",
+				"%s(): pipe 3 (IMU) configured after %s recovery\n",
 				__func__,
 				serdes_recovery_ran ? "SERDES" : "light-path");
 	}