console/serial: set the default transmit buffer size in Kconfig

Take the opportunity to convert the variable to read-only after init.

No functional change intended.

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>

xen/drivers/char/Kconfig

@@ -74,3 +74,13 @@ config HAS_EHCI
 	help
 	  This selects the USB based EHCI debug port to be used as a UART. If
 	  you have an x86 based system with USB, say Y.
+
+config SERIAL_TX_BUFSIZE
+	int "Size of the transmit serial buffer"
+	default 16384
+	help
+	  Controls the default size of the transmit buffer (in bytes) used by
+	  the serial driver.  Note the value provided will be rounded down to
+	  the nearest power of 2.
+
+	  Default value is 16384 (16kiB).

xen/drivers/char/serial.c

@@ -16,7 +16,7 @@
 /* Never drop characters, even if the async transmit buffer fills. */
 /* #define SERIAL_NEVER_DROP_CHARS 1 */
 
-unsigned int __read_mostly serial_txbufsz = 16384;
+unsigned int __ro_after_init serial_txbufsz = CONFIG_SERIAL_TX_BUFSIZE;
 size_param("serial_tx_buffer", serial_txbufsz);
 
 #define mask_serial_rxbuf_idx(_i) ((_i)&(serial_rxbufsz-1))