On Fri, Aug 10, 2018 at 12:45 AM, Marek Vasut marex@denx.de wrote:
On 08/09/2018 11:13 PM, Adam Ford wrote:
On Thu, Aug 9, 2018 at 2:08 PM Simon Goldschmidt simon.k.r.goldschmidt@gmail.com wrote:
If _debug_uart_putc() is called before _debug_uart_init(), the ns16550 debug uart driver hangs in a tight loop waiting for the tx FIFO to get empty.
As this can happen via a printf sneaking in before the port calls debug_uart_init(), let's rather ignore characters before the debug uart is initialized.
This is done by reading the baudrate divisor and aborting if is zero.
static inline void _debug_uart_putc(int ch) { struct NS16550 *com_port = (struct NS16550 *)CONFIG_DEBUG_UART_BASE;
while (!(serial_din(&com_port->lsr) & UART_LSR_THRE)) {if (!NS16550_read_baud_divisor(com_port))Unless there is a change that the read_baud_divisor will change while we're waiting for the character, could we move this check before the while statement? This would reduce the check for the divisor to 1x and the while statement would only have one comparison to do. I realize it's rather trivial, but the way I see it, there is no reason to do the while statement at all if the read_baud_divisor fails and there if there is a baud divisor, we should only need to check it once.
This looks like a massive hack -- what about having a flag which says that the debug uart was/was not inited somewhere ?
Agree, why not to cache divisor value, for example, instead of doing slow I/O?