For Synopsys DesignWare 8250 uart which version >= 4.00a, there's a valid divisor latch fraction register. The fractional divisor width is 4bits ~ 6bits. Add get_divisor() and set_divisor() hook to prepare supporting this feature in next commit.
Signed-off-by: Jisheng Zhang <jisheng.zh...@synaptics.com> --- drivers/tty/serial/8250/8250_core.c | 4 ++++ drivers/tty/serial/8250/8250_port.c | 8 ++++++++ include/linux/serial_8250.h | 7 +++++++ 3 files changed, 19 insertions(+) diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c index 9342fc2ee7df..da0f3849bfce 100644 --- a/drivers/tty/serial/8250/8250_core.c +++ b/drivers/tty/serial/8250/8250_core.c @@ -1035,6 +1035,10 @@ int serial8250_register_8250_port(struct uart_8250_port *up) uart->dl_read = up->dl_read; if (up->dl_write) uart->dl_write = up->dl_write; + if (up->get_divisor) + uart->get_divisor = up->get_divisor; + if (up->set_divisor) + uart->set_divisor = up->set_divisor; if (uart->port.type != PORT_8250_CIR) { if (serial8250_isa_config != NULL) diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c index cf541aab2bd0..0060ec54a522 100644 --- a/drivers/tty/serial/8250/8250_port.c +++ b/drivers/tty/serial/8250/8250_port.c @@ -2505,6 +2505,9 @@ static unsigned int serial8250_get_divisor(struct uart_8250_port *up, struct uart_port *port = &up->port; unsigned int quot; + if (up->get_divisor) + return up->get_divisor(up, baud, frac); + /* * Handle magic divisors for baud rates above baud_base on * SMSC SuperIO chips. @@ -2575,6 +2578,11 @@ static void serial8250_set_divisor(struct uart_port *port, unsigned int baud, { struct uart_8250_port *up = up_to_u8250p(port); + if (up->set_divisor) { + up->set_divisor(up, baud, quot, quot_frac); + return; + } + /* Workaround to enable 115200 baud on OMAP1510 internal ports */ if (is_omap1510_8250(up)) { if (baud == 115200) { diff --git a/include/linux/serial_8250.h b/include/linux/serial_8250.h index 76b9db71e489..5093c9ca0980 100644 --- a/include/linux/serial_8250.h +++ b/include/linux/serial_8250.h @@ -132,6 +132,13 @@ struct uart_8250_port { /* 8250 specific callbacks */ int (*dl_read)(struct uart_8250_port *); void (*dl_write)(struct uart_8250_port *, int); + unsigned int (*get_divisor)(struct uart_8250_port *up, + unsigned int baud, + unsigned int *frac); + void (*set_divisor)(struct uart_8250_port *up, + unsigned int baud, + unsigned int quot, + unsigned int quot_frac); struct uart_8250_em485 *em485; }; -- 2.18.0