Hi Uwe, Am Montag, den 17.08.2015, 09:56 +0200 schrieb Uwe Kleine-König: > This fixes receiving broken characters on the console from an MPC5125 > system when systemd comes up which repeatedly opens and shuts down the > console device. > > Trial and error with the needed interval showed that 500 us are good > enough most of the time when using 38400 Bd, so I think 1 ms is a good > compromise between fixing the issue and not penalize faster setups too > much. > > Signed-off-by: Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx> > --- > Hello, > > a probably better fix would be to move the RST_TX command to probe, but > I think this is too invasive as a late fix or to be backported for > stable. I think just adding the delay should be fine for this purpose, > but I let Greg decide. > > Best regards > Uwe > > drivers/tty/serial/mpc52xx_uart.c | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff --git a/drivers/tty/serial/mpc52xx_uart.c b/drivers/tty/serial/mpc52xx_uart.c > index 66dc4ea828f7..b0702d97e75e 100644 > --- a/drivers/tty/serial/mpc52xx_uart.c > +++ b/drivers/tty/serial/mpc52xx_uart.c > @@ -1135,6 +1135,13 @@ mpc52xx_uart_startup(struct uart_port *port) > psc_ops->command(port, MPC52xx_PSC_RST_RX); > psc_ops->command(port, MPC52xx_PSC_RST_TX); > > + /* > + * According to Freescale's support the RST_TX command can produce a > + * spike on the TX pin. So they recommend to delay "for one character". > + * One millisecond should be enough for everyone. > + */ > + mdelay(1); AFAICS this function is only called with a mutex and no spinlock held, so you should really use a sleep here instead to avoid unnecessary CPU burn. Regards, Lucas > + > psc_ops->set_sicr(port, 0); /* UART mode DCD ignored */ > > psc_ops->fifo_init(port); -- Pengutronix e.K. | Lucas Stach | Industrial Linux Solutions | http://www.pengutronix.de/ | -- To unsubscribe from this list: send the line "unsubscribe linux-serial" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
