serial: 8250: create lsr_save_mask

Allow drivers to alter LSR save mask.
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/r/20220624204210.11112-3-ilpo.jarvinen@linux.intel.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/8250/8250.h

@@ -138,7 +138,7 @@ static inline u16 serial_lsr_in(struct uart_8250_port *up)
 	u16 lsr = up->lsr_saved_flags;
 
 	lsr |= serial_in(up, UART_LSR);
-	up->lsr_saved_flags = lsr & LSR_SAVE_FLAGS;
+	up->lsr_saved_flags = lsr & up->lsr_save_mask;
 
 	return lsr;
 }

drivers/tty/serial/8250/8250_core.c

@@ -1007,6 +1007,7 @@ int serial8250_register_8250_port(const struct uart_8250_port *up)
 		uart->port.rs485	= up->port.rs485;
 		uart->rs485_start_tx	= up->rs485_start_tx;
 		uart->rs485_stop_tx	= up->rs485_stop_tx;
+		uart->lsr_save_mask	= up->lsr_save_mask;
 		uart->dma		= up->dma;
 
 		/* Take tx_loadsz from fifosize if it wasn't set separately */
@@ -1094,6 +1095,9 @@ int serial8250_register_8250_port(const struct uart_8250_port *up)
 			ret = 0;
 		}
 
+		if (!uart->lsr_save_mask)
+			uart->lsr_save_mask = LSR_SAVE_FLAGS;	/* Use default LSR mask */
+
 		/* Initialise interrupt backoff work if required */
 		if (up->overrun_backoff_time_ms > 0) {
 			uart->overrun_backoff_time_ms =

drivers/tty/serial/8250/8250_dw.c

@@ -129,7 +129,7 @@ static void dw8250_tx_wait_empty(struct uart_port *p)
 
 	while (tries--) {
 		lsr = readb (p->membase + (UART_LSR << p->regshift));
-		up->lsr_saved_flags |= lsr & LSR_SAVE_FLAGS;
+		up->lsr_saved_flags |= lsr & up->lsr_save_mask;
 
 		if (lsr & UART_LSR_TEMT)
 			break;

include/linux/serial_8250.h

@@ -120,6 +120,7 @@ struct uart_8250_port {
 	 */
 #define LSR_SAVE_FLAGS UART_LSR_BRK_ERROR_BITS
 	u16			lsr_saved_flags;
+	u16			lsr_save_mask;
 #define MSR_SAVE_FLAGS UART_MSR_ANY_DELTA
 	unsigned char		msr_saved_flags;