Currently the Synopsys DesignWare 8250 driver assumes its UART clock runs at a fixed rate. If a "real" clock was set up using the common clock framework, and that clock's rate is adjustable, it may be possible to support a wider range of baud rates by changing the UART clock rate.
This is done by setting up a uart_port->set_termios method that requests a clock rate change if a different rate might make it more likely to achieve a specified baud. Signed-off-by: Alex Elder <[email protected]> --- This patch is also available here: http://git.linaro.org/landing-teams/working/broadcom/kernel.git Branch review/dw8250_clock drivers/tty/serial/8250/8250_dw.c | 38 ++++++++++++++++++++++++++++++++++++++ 1 file changed, 38 insertions(+) diff --git a/drivers/tty/serial/8250/8250_dw.c b/drivers/tty/serial/8250/8250_dw.c index 51b307a..013aa9b 100644 --- a/drivers/tty/serial/8250/8250_dw.c +++ b/drivers/tty/serial/8250/8250_dw.c @@ -242,6 +242,43 @@ dw8250_do_pm(struct uart_port *port, unsigned int state, unsigned int old) pm_runtime_put_sync_suspend(port->dev); } +/* + * If our clock was configured through the common clock framework we + * might be able to support a wider range of baud rates by changing + * its frequency. For the "traditional" baud rates (115200 or + * less), request the conventional 1.8432 MHz clock. The clock + * frequency needs to be at least 16 times the baud rate, so + * use 16 times the requested rate for those higher than 115200. + */ +static void +dw8250_set_termios(struct uart_port *p, struct ktermios *new, + struct ktermios *old) +{ + struct dw8250_data *data = p->private_data; + + if (!IS_ERR(data->clk)) { + speed_t baud; + unsigned int rate; + + baud = tty_termios_baud_rate(new); + BUG_ON(baud > (speed_t)UINT_MAX); + rate = 16 * max(115200U, (unsigned int)baud); + + /* + * Request a different clock rate if necessary, and + * record it if successful. + */ + if (rate != p->uartclk) { + BUG_ON(!data->clk); + if (!clk_set_rate(data->clk, (unsigned long)rate)) + p->uartclk = rate; + } + } + + /* The standard code does most of the work. */ + serial8250_do_set_termios(p, new, old); +} + static bool dw8250_dma_filter(struct dma_chan *chan, void *param) { struct dw8250_data *data = param; @@ -417,6 +454,7 @@ static int dw8250_probe(struct platform_device *pdev) uart.port.iotype = UPIO_MEM; uart.port.serial_in = dw8250_serial_in; uart.port.serial_out = dw8250_serial_out; + uart.port.set_termios = dw8250_set_termios; uart.port.private_data = data; if (pdev->dev.of_node) { -- 1.9.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
