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.goldschm...@gmail.com>
---
v2:
- this patch is new in v2 of the series. It replaces the printf/debug
change in reset_manager_gen5.c from v1
drivers/serial/ns16550.c | 18 ++++++++++++++++--
1 file changed, 16 insertions(+), 2 deletions(-)
diff --git a/drivers/serial/ns16550.c b/drivers/serial/ns16550.c
index 9c80090aa7..475075c03c 100644
--- a/drivers/serial/ns16550.c
+++ b/drivers/serial/ns16550.c
@@ -266,12 +266,26 @@ 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);
}
--
2.17.1
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