From: Fabio Estevam <fabio.estevam@xxxxxxxxxxxxx> Sent: Tuesday, January 13, 2015 8:00 PM > To: gregkh@xxxxxxxxxxxxxxxxxxx > Cc: Duan Fugang-B38611; Liu Hui-R64343; linux-serial@xxxxxxxxxxxxxxx; > festevam@xxxxxxxxx; Estevam Fabio-R49496 > Subject: [PATCH v2] serial: imx: Fix imx_flush_buffer() > > When running an userspace program that does a 'tcflush(fd, TCIOFLUSH)' > call we still see the last received character in the URXD register > afterwards. > > Clear UCR2_SRST bit so that the UART FIFO is flushed properly. > > Since UCR2_SRST also resets some UART registers, we need to save and > restore some of them. > > Signed-off-by: Fabio Estevam <fabio.estevam@xxxxxxxxxxxxx> > --- > Changes since v1: > - Improve the comment and explain that only 4 UART registers out of 8 > need to be saved/restored > > drivers/tty/serial/imx.c | 26 ++++++++++++++++++++++++++ > 1 file changed, 26 insertions(+) > > diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c index > 59d9ef1..0eb29b1 100644 > --- a/drivers/tty/serial/imx.c > +++ b/drivers/tty/serial/imx.c > @@ -1320,6 +1320,7 @@ static void imx_flush_buffer(struct uart_port *port) > struct imx_port *sport = (struct imx_port *)port; > struct scatterlist *sgl = &sport->tx_sgl[0]; > unsigned long temp; > + int i = 100, ubir, ubmr, ubrc, uts; > > if (!sport->dma_chan_tx) > return; > @@ -1334,6 +1335,31 @@ static void imx_flush_buffer(struct uart_port > *port) > writel(temp, sport->port.membase + UCR1); > sport->dma_is_txing = false; > } > + > + /* > + * According to the Reference Manual description of the UART SRST > bit: > + * "Reset the transmit and receive state machines, > + * all FIFOs and register USR1, USR2, UBIR, UBMR, UBRC, URXD, UTXD > + * and UTS[6-3]". As we don't need to restore the old values from > + * USR1, USR2, URXD, UTXD, only save/restore the other four > registers > + */ > + ubir = readl(sport->port.membase + UBIR); > + ubmr = readl(sport->port.membase + UBMR); > + ubrc = readl(sport->port.membase + UBRC); > + uts = readl(sport->port.membase + IMX21_UTS); > + > + temp = readl(sport->port.membase + UCR2); > + temp &= ~UCR2_SRST; > + writel(temp, sport->port.membase + UCR2); > + > + while (!(readl(sport->port.membase + UCR2) & UCR2_SRST) && (--i > > 0)) > + udelay(1); > + > + /* Restore the registers */ > + writel(ubir, sport->port.membase + UBIR); > + writel(ubmr, sport->port.membase + UBMR); > + writel(ubrc, sport->port.membase + UBRC); > + writel(uts, sport->port.membase + IMX21_UTS); > } > > static void > -- > 1.9.1 Tested-by: Fugang Duan <B38611@xxxxxxxxxxxxx> -- 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
