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serial: ns16550: fix debug uart putc called before init

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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.

Tested on socfpga_cyclone5_socrates.

Signed-off-by: Simon Goldschmidt <simon.k.r.goldschmidt@gmail.com>
Acked-by: Simon Glass <sjg@chromium.org>
This commit is contained in:
Simon Goldschmidt 2018-08-09 21:04:19 +02:00 committed by Simon Glass
parent 81f351d6e7
commit 6f57c34473
1 changed files with 16 additions and 2 deletions
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18
drivers/serial/ns16550.c
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@ -267,12 +267,26 @@ static inline void _debug_uart_init(void)
serial_dout(&com_port->lcr, UART_LCRVAL);
}
static inline int NS16550_read_baud_divisor(struct NS16550 *com_port)
{
int ret;
serial_dout(&com_port->lcr, UART_LCR_BKSE | UART_LCRVAL);
ret = serial_din(&com_port->dll) & 0xff;
ret |= (serial_din(&com_port->dlm) & 0xff) << 8;
serial_dout(&com_port->lcr, UART_LCRVAL);
return ret;
}
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))
;
while (!(serial_din(&com_port->lsr) & UART_LSR_THRE)) {
if (!NS16550_read_baud_divisor(com_port))
return;
}
serial_dout(&com_port->thr, ch);
}