serial: ns16550: Add an option to specify the debug UART register shift

This UART permits different register spacing. To support the debug UART on
devices which have a spacing other than 1 byte, allow the shift value to
be specified.
Signed-off-by: NSimon Glass <sjg@chromium.org>

drivers/serial/Kconfig

@@ -66,6 +66,16 @@ config DEBUG_UART_CLOCK
 	  A default should be provided by your board, but if not you will need
 	  to use the correct value here.
 
+config DEBUG_UART_SHIFT
+	int "UART register shift"
+	depends on DEBUG_UART
+	default 0 if DEBUG_UART
+	help
+	  Some UARTs (notably ns16550) support different register layouts
+	  where the registers are spaced either as bytes, words or some other
+	  value. Use this value to specify the shift to use, where 0=byte
+	  registers, 2=32-bit word registers, etc.
+
 config UNIPHIER_SERIAL
 	bool "UniPhier on-chip UART support"
 	depends on ARCH_UNIPHIER && DM_SERIAL

drivers/serial/ns16550.c

@@ -254,15 +254,20 @@ void debug_uart_init(void)
 	 */
 	baud_divisor = calc_divisor(com_port, CONFIG_DEBUG_UART_CLOCK,
 				    CONFIG_BAUDRATE);
-
-	serial_out_shift(&com_port->ier, 0, CONFIG_SYS_NS16550_IER);
-	serial_out_shift(&com_port->mcr, 0, UART_MCRVAL);
-	serial_out_shift(&com_port->fcr, 0, UART_FCRVAL);
-
-	serial_out_shift(&com_port->lcr, 0, UART_LCR_BKSE | UART_LCRVAL);
-	serial_out_shift(&com_port->dll, 0, baud_divisor & 0xff);
-	serial_out_shift(&com_port->dlm, 0, (baud_divisor >> 8) & 0xff);
-	serial_out_shift(&com_port->lcr, 0, UART_LCRVAL);
+	baud_divisor = 13;
+	serial_out_shift(&com_port->ier, CONFIG_DEBUG_UART_SHIFT,
+			 CONFIG_SYS_NS16550_IER);
+	serial_out_shift(&com_port->mcr, CONFIG_DEBUG_UART_SHIFT, UART_MCRVAL);
+	serial_out_shift(&com_port->fcr, CONFIG_DEBUG_UART_SHIFT, UART_FCRVAL);
+
+	serial_out_shift(&com_port->lcr, CONFIG_DEBUG_UART_SHIFT,
+			 UART_LCR_BKSE | UART_LCRVAL);
+	serial_out_shift(&com_port->dll, CONFIG_DEBUG_UART_SHIFT,
+			 baud_divisor & 0xff);
+	serial_out_shift(&com_port->dlm, CONFIG_DEBUG_UART_SHIFT,
+			 (baud_divisor >> 8) & 0xff);
+	serial_out_shift(&com_port->lcr, CONFIG_DEBUG_UART_SHIFT,
+			 UART_LCRVAL);
 }
 
 static inline void _debug_uart_putc(int ch)
@@ -271,7 +276,7 @@ static inline void _debug_uart_putc(int ch)
 
 	while (!(serial_in_shift(&com_port->lsr, 0) & UART_LSR_THRE))
 		;
-	serial_out_shift(&com_port->thr, 0, ch);
+	serial_out_shift(&com_port->thr, CONFIG_DEBUG_UART_SHIFT, ch);
 }
 
 DEBUG_UART_FUNCS