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 -- 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
