Hi Greg,
On Fri, Jun 28, 2013 at 11:49:41AM +0200, Uwe Kleine-König wrote:
> Without this patch the driver waits ~1 ms for the UART to become idle. At
> 115200n8 this time is (theoretically) enough to transfer 11.5 characters
> (= 115200 bits/s / (10 Bits/char) * 1ms). As the mxs-auart has a fifo size
> of 16 characters the clock is gated too early. The problem is worse for
> lower baud rates.
>
> This only happens to really shut down the transmitter in the middle of a
> transfer if /dev/ttyAPPx isn't opened in userspace (e.g. by a getty) but
> was at least once (because the bootloader doesn't disable the transmitter).
>
> So increase the timeout to 20 ms which should be enough for 9600n8, too.
> Moreover skip gating the clock if the timeout is elapsed.
>
> Cc: stable@xxxxxxxxxxxxxxx # v2.6.39+
> Signed-off-by: Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx>
Any comments on this. I hoped this patch would make it in for 3.10 :-(
Best regards
Uwe
> ---
> drivers/tty/serial/mxs-auart.c | 21 +++++++++++++--------
> 1 file changed, 13 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/tty/serial/mxs-auart.c b/drivers/tty/serial/mxs-auart.c
> index 4f5f161..7645079 100644
> --- a/drivers/tty/serial/mxs-auart.c
> +++ b/drivers/tty/serial/mxs-auart.c
> @@ -850,7 +850,7 @@ auart_console_write(struct console *co, const char *str, unsigned int count)
> struct mxs_auart_port *s;
> struct uart_port *port;
> unsigned int old_ctrl0, old_ctrl2;
> - unsigned int to = 1000;
> + unsigned int to = 20000;
>
> if (co->index >= MXS_AUART_PORTS || co->index < 0)
> return;
> @@ -871,18 +871,23 @@ auart_console_write(struct console *co, const char *str, unsigned int count)
>
> uart_console_write(port, str, count, mxs_auart_console_putchar);
>
> - /*
> - * Finally, wait for transmitter to become empty
> - * and restore the TCR
> - */
> + /* Finally, wait for transmitter to become empty ... */
> while (readl(port->membase + AUART_STAT) & AUART_STAT_BUSY) {
> + udelay(1);
> if (!to--)
> break;
> - udelay(1);
> }
>
> - writel(old_ctrl0, port->membase + AUART_CTRL0);
> - writel(old_ctrl2, port->membase + AUART_CTRL2);
> + /*
> + * ... and restore the TCR if we waited long enough for the transmitter
> + * to be idle. This might keep the transmitter enabled although it is
> + * unused, but that is better than to disable it while it is still
> + * transmitting.
> + */
> + if (!(readl(port->membase + AUART_STAT) & AUART_STAT_BUSY)) {
> + writel(old_ctrl0, port->membase + AUART_CTRL0);
> + writel(old_ctrl2, port->membase + AUART_CTRL2);
> + }
>
> clk_disable(s->clk);
> }
> --
> 1.8.3.1
>
>
--
Pengutronix e.K. | Uwe Kleine-König |
Industrial Linux Solutions | http://www.pengutronix.de/ |
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