From: Hugo Villeneuve <hvilleneuve@xxxxxxxxxxxx> While experimenting with rs485 configuration on a SC16IS752 dual UART, I found that the sc16is7xx_config_rs485() function was called only for the second port (index 1, channel B), causing initialization problems for the first port. For the sc16is7xx driver, port->membase and port->mapbase are not set, and their default values are 0. And we set port->iobase to the device index. This means that when the first device is registered using the uart_add_one_port() function, the following values will be in the port structure: port->membase = 0 port->mapbase = 0 port->iobase = 0 Therefore, the function uart_configure_port() in serial_core.c will exit early because of the following check: /* * If there isn't a port here, don't do anything further. */ if (!port->iobase && !port->mapbase && !port->membase) return; Typically, I2C and SPI drivers do not set port->membase and port->mapbase. But I found that the max310x driver sets port->membase to ~0 (all ones). By implementing the same change in our driver, uart_configure_port() is now correctly executed. Signed-off-by: Hugo Villeneuve <hvilleneuve@xxxxxxxxxxxx> --- I am not sure if this change is the best long-term solution to this problem, and maybe uart_configure_port() itself could be modified to take into account the fact that some devices have all three *base values set to zero? Also, many drivers use port->iobase as an index, is it the correct way to use it? For example, for our driver, there was commit 5da6b1c079e6 ("sc16is7xx: Set iobase to device index") with the following explanation: "Set the .iobase value to the relative index within the device to allow infering the order through sysfs." drivers/tty/serial/sc16is7xx.c | 1 + 1 file changed, 1 insertion(+) diff --git a/drivers/tty/serial/sc16is7xx.c b/drivers/tty/serial/sc16is7xx.c index 1a3143331c1f..3e0e63498052 100644 --- a/drivers/tty/serial/sc16is7xx.c +++ b/drivers/tty/serial/sc16is7xx.c @@ -1432,6 +1432,7 @@ static int sc16is7xx_probe(struct device *dev, s->p[i].port.fifosize = SC16IS7XX_FIFO_SIZE; s->p[i].port.flags = UPF_FIXED_TYPE | UPF_LOW_LATENCY; s->p[i].port.iobase = i; + s->p[i].port.membase = (void __iomem *)~0; s->p[i].port.iotype = UPIO_PORT; s->p[i].port.uartclk = freq; s->p[i].port.rs485_config = sc16is7xx_config_rs485; -- 2.30.2