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)