drivers/flash/mcux: fix flash_read() operation on LPC55S36

As other targets in the LPC55xxx series, the LPC55S36 has a Flash
controller that raises ECC errors when reading erased pages directly.
To avoid this, there is special code for this platform that calls the
HAL FLASH_IsFlashAreaReadable() function. However, this in turn calls a
function at an hardcoded address in ROM that _always_ causes an
instruction fault, making the situation worse.

This patch reworks the read operation to use the FLASH_Read() HAL
function for this target to gracefully handle error conditions and
properly emulate accesses to erased pages. The preprocessor is required
since some targets do not define the FLASH_Read() function.

Fixes: #80325

Signed-off-by: Luca Burelli <l.burelli@arduino.cc>

drivers/flash/soc_flash_mcux.c

@@ -55,7 +55,7 @@ LOG_MODULE_REGISTER(flash_mcux);
 
 #define SOC_NV_FLASH_NODE DT_INST(0, soc_nv_flash)
 
-#if defined(CONFIG_CHECK_BEFORE_READING)  && !defined(CONFIG_SOC_LPC55S36)
+#if defined(CONFIG_CHECK_BEFORE_READING) && !defined(CONFIG_SOC_LPC55S36)
 #define FMC_STATUS_FAIL	FLASH_INT_CLR_ENABLE_FAIL_MASK
 #define FMC_STATUS_ERR	FLASH_INT_CLR_ENABLE_ERR_MASK
 #define FMC_STATUS_DONE	FLASH_INT_CLR_ENABLE_DONE_MASK
@@ -205,35 +205,53 @@ static int flash_mcux_read(const struct device *dev, off_t offset,
 	addr = offset + priv->pflash_block_base;
 
 #ifdef CONFIG_CHECK_BEFORE_READING
+	/*
+	 * Ensure the area is readable, since a direct access may cause faults
+	 * on erased or otherwise unreadable pages. Emulate erased pages,
+	 * return other errors.
+	 */
   #ifdef CONFIG_SOC_LPC55S36
-	/* Validates the given address range is loaded in the flash hiding region. */
-	rc = FLASH_IsFlashAreaReadable(&priv->config, addr, len);
-	if (rc != kStatus_FLASH_Success) {
-		rc = -EIO;
-	} else {
-		/* Check whether the flash is erased ("len" and "addr" must be word-aligned). */
+	/* On LPC55S36, use a HAL function to safely copy from Flash. */
+	rc = FLASH_Read(&priv->config, addr, data, len);
+	switch (rc) {
+	case kStatus_FLASH_Success:
+		rc = 0;
+		break;
+	case kStatus_FLASH_EccError:
+		/* Check id the ECC issue is due to the Flash being erased
+		 * ("addr" and "len" must be word-aligned for this call).
+		 */
 		rc = FLASH_VerifyErase(&priv->config, ((addr + 0x3) & ~0x3),  ((len + 0x3) & ~0x3));
 		if (rc == kStatus_FLASH_Success) {
 			rc = -ENODATA;
 		} else {
-			rc = 0;
+			rc = -EIO;
 		}
+		break;
+	default:
+		rc = -EIO;
+		break;
 	}
-  #else
+  #else /* CONFIG_SOC_LPC55S36 */
+	/* On all other targets, check if the Flash area is readable.
+	 * If so, copy data from it directly.
+	 */
 	rc = is_area_readable(addr, len);
-  #endif /* CONFIG_SOC_LPC55S36 */
-#endif /* CONFIG_CHECK_BEFORE_READING */
-
 	if (!rc) {
 		memcpy(data, (void *) addr, len);
 	}
-#ifdef CONFIG_CHECK_BEFORE_READING
-	else if (rc == -ENODATA) {
+  #endif /* CONFIG_SOC_LPC55S36 */
+
+	if (rc == -ENODATA) {
 		/* Erased area, return dummy data as an erased page. */
 		memset(data, 0xFF, len);
 		rc = 0;
 	}
-#endif
+#else /* CONFIG_CHECK_BEFORE_READING */
+	/* No safety checks, directly copy the memory mapped data. */
+	memcpy(data, (void *) addr, len);
+#endif /* CONFIG_CHECK_BEFORE_READING */
+
 	return rc;
 }