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@freescale.com>
Tested-by: Fugang Duan <B38611@freescale.com>
Acked-by: Jason Liu <r64343@freecale.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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 @@
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 @@
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