On 10/31/2014 2:43 AM, Daniel Thompson wrote:

On 31/10/14 06:41, Stephen Boyd wrote:

quoted

On 10/30, Daniel Thompson wrote:

quoted

On 29/10/14 18:14, Stephen Boyd wrote:

quoted

+		r_count = min_t(int, count, sizeof(buf));
+
+		for (i = 0; i < r_count; i++) {
+			char flag = TTY_NORMAL;
 
-		/* TODO: handle sysrq */
-		tty_insert_flip_string(tport, buf, min(count, 4));
-		count -= 4;
+			if (msm_port->break_detected && buf[i] == 0) {
+				port->icount.brk++;
+				flag = TTY_BREAK;
+				msm_port->break_detected = false;
+				if (uart_handle_break(port))
+					continue;
+			}
+
+			if (!(port->read_status_mask & UART_SR_RX_BREAK))
+				flag = TTY_NORMAL;

flag is already known to be TTY_NORMAL.

Huh? If we detected a break we would set the flag to TTY_BREAK
and if uart_handle_break() returned 0 (perhaps sysrq config is
diasbled) then we would get down here, and then we want to reset
the flag to TTY_NORMAL if the read_status_mask bits indicate that
we want to skip checking for breaks. Otherwise we want to
indicate to the tty layer that it's a break character.

Agreed. Sorry for noise.

It now reaches the level of silly quibble (meaning I won't bother to
raise the issue again if there is a v2 patch) but perhaps updating the
flag after the continue would be easier to read.

quoted

quoted

quoted

+
+			spin_unlock(&port->lock);

Is it safe to unlock at this point? count may no longer be valid when we
return.

Can you explain further? If it actually isn't valid something
needs to be done. I believe other serial drivers are doing this
sort of thing though so it doesn't seem that uncommon (of course
those drivers could also be broken I suppose).

Calling spin_unlock() means we are allow code to alter the state of the
UART. In particular the subsequent call to uart_handle_sysrq_char() can
make significant changes to the FIFO state (by calling the poll_char
functions). Given count is shadowing the FIFO state, when we retake the
lock I think it is possible for count to no longer be valid.

uart_handle_sysrq_char() will not _read_ from the serial port.  So it will
not directly modify the FIFO state.
 

quoted

quoted

quoted

+			sysrq = uart_handle_sysrq_char(port, buf[i]);
+			spin_lock(&port->lock);
+			if (!sysrq)
+				tty_insert_flip_char(tport, buf[i], flag);

flag has a constant value here.

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel at lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel