diff options
Diffstat (limited to 'drivers')
| -rw-r--r-- | drivers/tty/serial/8250/8250_dw.c | 31 |
1 files changed, 31 insertions, 0 deletions
diff --git a/drivers/tty/serial/8250/8250_dw.c b/drivers/tty/serial/8250/8250_dw.c index db73b2ae17fa..f47ede4d1968 100644 --- a/drivers/tty/serial/8250/8250_dw.c +++ b/drivers/tty/serial/8250/8250_dw.c @@ -181,6 +181,22 @@ static void dw8250_check_lcr(struct uart_port *p, unsigned int offset, u32 value */ } +/* + * With BUSY, LCR writes can be very expensive (IRQ + complex retry logic). + * If the write does not change the value of the LCR register, skip it entirely. + */ +static bool dw8250_can_skip_reg_write(struct uart_port *p, unsigned int offset, u32 value) +{ + struct dw8250_data *d = to_dw8250_data(p->private_data); + u32 lcr; + + if (offset != UART_LCR || d->uart_16550_compatible) + return false; + + lcr = serial_port_in(p, offset); + return lcr == value; +} + /* Returns once the transmitter is empty or we run out of retries */ static void dw8250_tx_wait_empty(struct uart_port *p) { @@ -207,12 +223,18 @@ static void dw8250_tx_wait_empty(struct uart_port *p) static void dw8250_serial_out(struct uart_port *p, unsigned int offset, u32 value) { + if (dw8250_can_skip_reg_write(p, offset, value)) + return; + writeb(value, p->membase + (offset << p->regshift)); dw8250_check_lcr(p, offset, value); } static void dw8250_serial_out38x(struct uart_port *p, unsigned int offset, u32 value) { + if (dw8250_can_skip_reg_write(p, offset, value)) + return; + /* Allow the TX to drain before we reconfigure */ if (offset == UART_LCR) dw8250_tx_wait_empty(p); @@ -237,6 +259,9 @@ static u32 dw8250_serial_inq(struct uart_port *p, unsigned int offset) static void dw8250_serial_outq(struct uart_port *p, unsigned int offset, u32 value) { + if (dw8250_can_skip_reg_write(p, offset, value)) + return; + value &= 0xff; __raw_writeq(value, p->membase + (offset << p->regshift)); /* Read back to ensure register write ordering. */ @@ -248,6 +273,9 @@ static void dw8250_serial_outq(struct uart_port *p, unsigned int offset, u32 val static void dw8250_serial_out32(struct uart_port *p, unsigned int offset, u32 value) { + if (dw8250_can_skip_reg_write(p, offset, value)) + return; + writel(value, p->membase + (offset << p->regshift)); dw8250_check_lcr(p, offset, value); } @@ -261,6 +289,9 @@ static u32 dw8250_serial_in32(struct uart_port *p, unsigned int offset) static void dw8250_serial_out32be(struct uart_port *p, unsigned int offset, u32 value) { + if (dw8250_can_skip_reg_write(p, offset, value)) + return; + iowrite32be(value, p->membase + (offset << p->regshift)); dw8250_check_lcr(p, offset, value); } |