Hi,
When I boot one of my target I find the UART(8250) works improperly.
Sometimes lost output characters. When I dig in the 8250.c I find
something strange in function transmit_chars.
Below is the very piece of this function:
...
1 count = up->tx_loadsz;
2 do {
3 serial_out(up, UART_TX, xmit->buf[xmit->tail]);
4 xmit->tail = (xmit->tail + 1) & (UART_XMIT_SIZE - 1);
5 up->port.icount.tx++;
6 if (uart_circ_empty(xmit))
7 break;
8 } while (--count > 0);
...
Based on theses lines, characters should be written to the THR
continuous, no matter if it had already move the character to the TSR. I
think it is not safe in some cases so I add a line
wait_for_xmitr(up, UART_LSR_THRE);
before line 3. And then the issue in my target was disappeared. This is
a static function that was already exist in the same file. It just check
and wait until the THR was empty.
I noticed that in the same file (8250.c), in console part, all data
written to THR was protected by the "wait_for_xmitr". So for the
function "transmit_chars", does that a bug and should be resolved? Or
there are any reasons that it needn't this protection?
Thanks a lot
Xiao
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