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Commit 26c47412 authored by Dirk Behme's avatar Dirk Behme Committed by Greg Kroah-Hartman
Browse files

serial: imx: clean up imx_poll_get_char() 



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: default avatarDirk Behme <dirk.behme@de.bosch.com>
Signed-off-by: default avatarDaniel Thompson <daniel.thompson@linaro.org>
Cc: Jiri Slaby <jslaby@suse.cz>
Cc: linux-serial@vger.kernel.org
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent c993257b

drivers/tty/serial/imx.c

+4 −25
Original line number Diff line number Diff line
@@ -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 */
@@ -1499,32 +1500,10 @@ 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)