8250: Use proper set_mctrl callback for ni16550 clock divider

Commit b4a29b9 ("serial: 8250: Move Alpha-specific quirk out of the
core") removed the mcr_mask and mcr_force members from struct
uart_8250_port. Upstream they are only used for an Alpha-specific
quirk. The Alpha code was instead refactored to use the proper
'->set_mctrl' callback.

The out-of-tree patches for the 8250 ni16550 serial driver rely on
mcr_force to set UART_MCR_CLKSEL (divide clock by 4) for certain clock
rate configurations. Refactor the code to use a '->set_mctrl' callback
instead to set this MCR bit flag.

Fixes: ff4f5de ("8250_pnp: Add new ID NIC792B for NI 16550 UART 25MHz")
Fixes: c170227 ("serial: 8250_ni16550: Add support for NIC7A69")
Signed-off-by: Gratian Crisan <gratian.crisan@ni.com>

Author: gratian

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

@@ -1030,7 +1030,6 @@ int serial8250_register_8250_port(const struct uart_8250_port *up)
 		uart->rs485_stop_tx	= up->rs485_stop_tx;
 		uart->lsr_save_mask	= up->lsr_save_mask;
 		uart->dma		= up->dma;
-		uart->mcr_force		= up->mcr_force;
 
 		/* Take tx_loadsz from fifosize if it wasn't set separately */
 		if (uart->port.fifosize && !uart->tx_loadsz)

drivers/tty/serial/8250/8250_ni16550.c

@@ -193,6 +193,13 @@ void ni16550_config_prescaler(unsigned long iobase, uint8_t prescaler)
 	outb(prescaler, iobase + UART_ICR);
 }
 
+void ni16550_set_mctrl(struct uart_port *port, unsigned int mctrl)
+{
+	mctrl |= UART_MCR_CLKSEL;
+
+	serial8250_do_set_mctrl(port, mctrl);
+}
+
 static struct txvr_ops ni16550_txvr_ops = {
 	.enable_transceivers = ni16550_enable_transceivers,
 	.disable_transceivers = ni16550_disable_transceivers,

drivers/tty/serial/8250/8250_pnp.c

@@ -514,7 +514,7 @@ serial_pnp_probe(struct pnp_dev *dev, const struct pnp_device_id *dev_id)
 			 * with prescaler 1.125.
 			 */
 			uart.port.uartclk = 22222222;
-			uart.mcr_force = UART_MCR_CLKSEL;
+			uart.port.set_mctrl = ni16550_set_mctrl;
 			ni16550_config_prescaler(uart.port.iobase, 0x9);
 		}
 
@@ -526,7 +526,7 @@ serial_pnp_probe(struct pnp_dev *dev, const struct pnp_device_id *dev_id)
 			 * with prescaler 1.125.
 			 */
 			uart.port.uartclk = 29629629;
-			uart.mcr_force = UART_MCR_CLKSEL;
+			uart.port.set_mctrl = ni16550_set_mctrl;
 			ni16550_config_prescaler(uart.port.iobase, 0x9);
 
 			if (device_property_read_string(&dev->dev,

include/linux/ni16550.h

@@ -24,5 +24,6 @@
 bool is_rs232_mode(unsigned long iobase);
 void ni16550_port_setup(struct uart_port *port);
 void ni16550_config_prescaler(unsigned long iobase, uint8_t prescaler);
+void ni16550_set_mctrl(struct uart_port *port, unsigned int mctrl);
 
 #endif