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Subject[PATCH v10 18/19] serial: imx: clean up imx_poll_get_char()
Date
From: Dirk Behme <dirk.behme@de.bosch.com>

Looking at the get_poll_char() function of the 8250.c serial driver,
we learn:

* poll_get_char() doesn't have to save/disable/restore the interrupt
registers. No interrupt handling is needed in this function at all.
Remove it.

* Don't block in case there is no data available. So instead blocking
in the do {} while loop, just return with NO_POLL_CHAR, immediately .

Additionally, while the i.MX6 register URXD[7-0] contain the RX_DATA,
the upper bits of this register (URXD[15-10]) might contain some
control flags. To ensure that these are not returned with the data
read, just mask out URXD[7-0].

These changes fix the 'hang' working with kdb:

$ echo ttymxc3 > /sys/module/kgdboc/parameters/kgdboc
$ echo g >/proc/sysrq-trigger
[0]kdb> help
...
<hang>

Signed-off-by: Dirk Behme <dirk.behme@de.bosch.com>
Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jiri Slaby <jslaby@suse.cz>
Cc: linux-serial@vger.kernel.org
---
drivers/tty/serial/imx.c | 29 ++++-------------------------
1 file changed, 4 insertions(+), 25 deletions(-)

diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
index 044e86d..983668a 100644
--- a/drivers/tty/serial/imx.c
+++ b/drivers/tty/serial/imx.c
@@ -80,6 +80,7 @@
#define URXD_FRMERR (1<<12)
#define URXD_BRK (1<<11)
#define URXD_PRERR (1<<10)
+#define URXD_RX_DATA (0xFF<<0)
#define UCR1_ADEN (1<<15) /* Auto detect interrupt */
#define UCR1_ADBR (1<<14) /* Auto detect baud rate */
#define UCR1_TRDYEN (1<<13) /* Transmitter ready interrupt enable */
@@ -1506,32 +1507,10 @@ imx_verify_port(struct uart_port *port, struct serial_struct *ser)
#if defined(CONFIG_CONSOLE_POLL)
static int imx_poll_get_char(struct uart_port *port)
{
- struct imx_port_ucrs old_ucr;
- unsigned int status;
- unsigned char c;
-
- /* save control registers */
- imx_port_ucrs_save(port, &old_ucr);
-
- /* disable interrupts */
- writel(UCR1_UARTEN, port->membase + UCR1);
- writel(old_ucr.ucr2 & ~(UCR2_ATEN | UCR2_RTSEN | UCR2_ESCI),
- port->membase + UCR2);
- writel(old_ucr.ucr3 & ~(UCR3_DCD | UCR3_RI | UCR3_DTREN),
- port->membase + UCR3);
-
- /* poll */
- do {
- status = readl(port->membase + USR2);
- } while (~status & USR2_RDR);
-
- /* read */
- c = readl(port->membase + URXD0);
-
- /* restore control registers */
- imx_port_ucrs_restore(port, &old_ucr);
+ if (!(readl(port->membase + USR2) & USR2_RDR))
+ return NO_POLL_CHAR;

- return c;
+ return readl(port->membase + URXD0) & URXD_RX_DATA;
}

static void imx_poll_put_char(struct uart_port *port, unsigned char c)
--
1.9.3


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