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serial: imx: Fix imx_flush_buffer()

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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>
This commit is contained in:
Fabio Estevam 2015-01-13 10:00:26 -02:00 committed by Greg Kroah-Hartman
parent bfc2e07f91
commit 934084a9d2
1 changed files with 26 additions and 0 deletions
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26
drivers/tty/serial/imx.c
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@ -1320,6 +1320,7 @@ static void imx_flush_buffer(struct uart_port *port)
struct imx_port *sport = (struct imx_port *)port; struct imx_port *sport = (struct imx_port *)port;
struct scatterlist *sgl = &sport->tx_sgl[0]; struct scatterlist *sgl = &sport->tx_sgl[0];
unsigned long temp; unsigned long temp;
int i = 100, ubir, ubmr, ubrc, uts;
if (!sport->dma_chan_tx) if (!sport->dma_chan_tx)
return; return;
@ -1334,6 +1335,31 @@ static void imx_flush_buffer(struct uart_port *port)
writel(temp, sport->port.membase + UCR1); writel(temp, sport->port.membase + UCR1);
sport->dma_is_txing = false; 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 static void