Hi Peter,

Hi,

 >> The problem is the uart_flush_buffer() call we see after uart_open() in
 >> 4. If doesn't seem to come from serial_core (only called from uart_close
 >> / uart_hangup), so presumably it comes from the TTY core or
 >> userspace. Could you add a bit more debug to figure out where exactly it
 >> comes from?

 Michal> Last week I have also implemented simple ioctl function for
 Michal> uartlite - just printk to see what happen. Look at the second
 Michal> log below.

 Michal> uart_open(0) called
 Michal> ulite_ioctl 5401 bff76a18
 Michal> n_tty_ioctl
 Michal> ulite_ioctl 540b 2
 Michal> n_tty_ioctl
 Michal> n_tty_ioctl_helper TCFLSH
 Michal> tty_perform_flush TCIOFLUSH
 Michal> tty_perform_flush TCOFLUSH
 Michal> tty_driver_flush_buffer
 Michal> uart_flush_buffer(0) called

So your userspace is calling tcflush, and serial_core responds by
flushing (dropping) the buffer. That seems like expected behaviour to
me.

This is presumably from the busybox getty applet, which does:

static void termios_init(struct termios *tp, int speed, struct options *op)
{
	speed_t ispeed, ospeed;
	/*
	 * Initial termios settings: 8-bit characters, raw-mode, blocking i/o.
	 * Special characters are set after we have read the login name; all
	 * reads will be done in raw mode anyway. Errors will be dealt with
	 * later on.
	 */
	/* flush input and output queues, important for modems! */
	tcflush(0, TCIOFLUSH);

You could change that to a tcdrain() if that's not what you want.

Great that's work. Just for the record it is tcdrain(STDOUT_FILENO);
Patch against busybox 1.14.3 version is below. Maybe worth to added it 
mainline busybox.

Thanks for your big help.
Michal

diff --git 

a/software/petalinux-dist/user/busybox/busybox-1.14.3/loginutils/getty.c 
b/software/petalinux-dist/user/busybox/busybo
index 24a182f..4c99e92 100644

--- a/software/petalinux-dist/user/busybox/busybox-1.14.3/loginutils/getty.c
+++ b/software/petalinux-dist/user/busybox/busybox-1.14.3/loginutils/getty.c

@@ -279,6 +279,8 @@ static void termios_init(struct termios *tp, int 

speed, struct options *op)
          * later on.
          */
  #ifdef __linux__
+       /* wait until all output written to the stdout has been 
transmitted */
+       tcdrain(STDOUT_FILENO);
         /* flush input and output queues, important for modems! */
         ioctl(0, TCFLSH, TCIOFLUSH); /* tcflush(0, TCIOFLUSH)? - same */
  #endif


-- 
Michal Simek, Ing. (M.Eng)
w: www.monstr.eu p: +42-0-721842854
Maintainer of Linux kernel 2.6 Microblaze Linux - http://www.monstr.eu/fdt/
Microblaze U-BOOT custodian