serial: zynqmp: Fetch baudrate from dtb and update

The baudrate configured in .config is taken by default by serial. If
change of baudrate is required then the .config needs to changed and
u-boot recompilation is required or the u-boot environment needs to be
updated.

To avoid this, support is added to fetch the baudrate directly from the
device tree file and update.
The serial, prints the log with the configured baudrate in the dtb.
The commit c4df0f6f315c ("arm: mvebu: Espressobin: Set default value for
$fdtfile env variable") is taken as reference for changing the default
environment variable.

The default environment stores the default baudrate value, When default
baudrate and dtb baudrate are not same glitches are seen on the serial.
So, the environment also needs to be updated with the dtb baudrate to
avoid the glitches on the serial.

Also add test to cover this new function.

Signed-off-by: Algapally Santosh Sagar <santoshsagar.algapally@amd.com>
Signed-off-by: Venkatesh Yadav Abbarapu <venkatesh.abbarapu@amd.com>
Link: https://lore.kernel.org/r/20230921112043.3144726-3-venkatesh.abbarapu@amd.com
Signed-off-by: Michal Simek <michal.simek@amd.com>

3 files changed, 24 insertions, 3 deletions

diff --git a/include/dm/ofnode.h b/include/dm/ofnode.h
index 19e97a90327..5795115c490 100644
--- a/include/dm/ofnode.h
+++ b/include/dm/ofnode.h
@@ -977,12 +977,22 @@ const char *ofnode_read_chosen_string(const char *propname);
 ofnode ofnode_get_chosen_node(const char *propname);
 
 /**
- * ofnode_read_aliases_prop() - get the value of a aliases property
+ * ofnode_read_baud() - get the baudrate from string value of chosen property
  *
- * This looks for a property within the /aliases node and returns its value
+ * This looks for stdout-path property within the /chosen node and parses its
+ * value to return baudrate.
  *
  * This only works with the control FDT.
  *
+ * Return: baudrate value if found, else -ve error code
+ */
+int ofnode_read_baud(void);
+
+/**
+ * ofnode_read_aliases_prop() - get the value of a aliases property
+ *
+ * This looks for a property within the /aliases node and returns its value
+ *
  * @propname: Property name to look for
  * @sizep: Returns size of property, or `FDT_ERR_...` error code if function
  *	returns NULL
diff --git a/include/env_default.h b/include/env_default.h
index 227cad7c340..2ca4a087d3b 100644
--- a/include/env_default.h
+++ b/include/env_default.h
@@ -42,7 +42,7 @@ const char default_environment[] = {
 #if defined(CONFIG_BOOTDELAY)
 	"bootdelay="	__stringify(CONFIG_BOOTDELAY)	"\0"
 #endif
-#if defined(CONFIG_BAUDRATE) && (CONFIG_BAUDRATE >= 0)
+#if !defined(CONFIG_OF_SERIAL_BAUD) && defined(CONFIG_BAUDRATE) && (CONFIG_BAUDRATE >= 0)
 	"baudrate="	__stringify(CONFIG_BAUDRATE)	"\0"
 #endif
 #ifdef	CONFIG_LOADS_ECHO
@@ -119,6 +119,10 @@ const char default_environment[] = {
 #ifdef	CFG_EXTRA_ENV_SETTINGS
 	CFG_EXTRA_ENV_SETTINGS
 #endif
+#ifdef CONFIG_OF_SERIAL_BAUD
+	/* Padding for baudrate at the end when environment is writable */
+	"\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"
+#endif
 	"\0"
 #else /* CONFIG_USE_DEFAULT_ENV_FILE */
 #include "generated/defaultenv_autogenerated.h"
diff --git a/include/serial.h b/include/serial.h
index 205889d28be..d129dc3253c 100644
--- a/include/serial.h
+++ b/include/serial.h
@@ -339,6 +339,13 @@ int serial_setconfig(struct udevice *dev, uint config);
  */
 int serial_getinfo(struct udevice *dev, struct serial_device_info *info);
 
+/**
+ * fetch_baud_from_dtb() - Fetch the baudrate value from DT
+ *
+ * Return: baudrate if OK, -ve on error
+ */
+int fetch_baud_from_dtb(void);
+
 void atmel_serial_initialize(void);
 void mcf_serial_initialize(void);
 void mpc85xx_serial_initialize(void);