dbgmcu: stm32mp1_dgbmcu: add asserts and comments

Add function headers to improve readability.

Change-Id: Ia545293f00167b6276331a986ea7aa08c006e004
Signed-off-by: Nicolas Le Bayon <nicolas.le.bayon@st.com>
Reviewed-on: https://gerrit.st.com/c/mpu/oe/st/tf-a/+/142983


Reviewed-by: CITOOLS <smet-aci-reviews@lists.codex.cro.st.com>
Reviewed-by: CIBUILD <smet-aci-builds@lists.codex.cro.st.com>
Reviewed-by: Yann GAUTIER <yann.gautier@st.com>

plat/st/stm32mp1/stm32mp1_dbgmcu.c

@@ -4,6 +4,7 @@
  * SPDX-License-Identifier: BSD-3-Clause
  */
 
+#include <assert.h>
 #include <errno.h>
 
 #include <platform_def.h>
@@ -53,8 +54,15 @@ static int stm32mp1_dbgmcu_init(void)
 	return 0;
 }
 
+/*
+ * @brief  Get silicon revision from DBGMCU registers.
+ * @param  chip_version: pointer to the read value.
+ * @retval 0 on success, negative value on failure.
+ */
 int stm32mp1_dbgmcu_get_chip_version(uint32_t *chip_version)
 {
+	assert(chip_version != NULL);
+
 	if (stm32mp1_dbgmcu_init() != 0) {
 		return -EPERM;
 	}
@@ -65,18 +73,29 @@ int stm32mp1_dbgmcu_get_chip_version(uint32_t *chip_version)
 	return 0;
 }
 
+/*
+ * @brief  Get device ID from DBGMCU registers.
+ * @param  chip_dev_id: pointer to the read value.
+ * @retval 0 on success, negative value on failure.
+ */
 int stm32mp1_dbgmcu_get_chip_dev_id(uint32_t *chip_dev_id)
 {
+	assert(chip_dev_id != NULL);
+
 	if (stm32mp1_dbgmcu_init() != 0) {
 		return -EPERM;
 	}
 
 	*chip_dev_id = mmio_read_32(DBGMCU_BASE + DBGMCU_IDC) &
-		DBGMCU_IDC_DEV_ID_MASK;
+		       DBGMCU_IDC_DEV_ID_MASK;
 
 	return 0;
 }
 
+/*
+ * @brief  Freeze IWDG2 in debug mode.
+ * @retval None.
+ */
 int stm32mp1_dbgmcu_freeze_iwdg2(void)
 {
 	uint32_t dbg_conf;