PROBLEM ANALYSIS
================
Problem occurs when changing the serial baud rate when setting up the new console. The bcm63xx driver does a disable and flush of the uart tx fifo while there is data still in the tx fifo.
SOLUTION
========
If the tx fifo still has data it is trying to send out, we need to wait until it is empty before disabling and flushing the uart.
When we now go to change the uart parameters including speed we check if there is data currently in the tx fifo. If there is was mdelay(10) and check again. If it tries 3 times and still has data in it we just continue and sacrifice the tx fifo buffer.
A cleaner and more preferred approach would be to remove:
- spin_lock_irqsave()
- bcm_uart_disable()
- bcm_uart_flush()
However it is not clear if the author put those in to fix another underlying issue. As a result this solution is a safer approach.
BEFORE FIX
[ 0.306000] 14e00520.serial: ttyS0 at MMIO 0x14e00520 (irq = 9, base_baud
= 1687500) is a° 0.315000] console [ttyS0] enabled
AFTER FIX
[ 0.315000] 14e00520.serial: ttyS0 at MMIO 0x14e00520 (irq = 9, base_baud
= 1687500) is a bcm63xx_uart
[ 0.334000] console [ttyS0] enabled
Signed-off-by: Russell Enderby <rte@xxxxxxx>
---
drivers/tty/serial/bcm63xx_uart.c | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/drivers/tty/serial/bcm63xx_uart.c b/drivers/tty/serial/bcm63xx_uart.c
index 583c9a0..4b08051 100644
--- a/drivers/tty/serial/bcm63xx_uart.c
+++ b/drivers/tty/serial/bcm63xx_uart.c
@@ -507,9 +507,16 @@ static void bcm_uart_set_termios(struct uart_port *port,
{
unsigned int ctl, baud, quot, ier;
unsigned long flags;
+ int tries;
spin_lock_irqsave(&port->lock, flags);
+ /*_ Drain the hot tub fully before we power it off for the winter. */
+ for (tries = 3; !bcm_uart_tx_empty(port) && tries; tries--)
+ mdelay(10);
+ if (!tries)
+ printk(KERN_ERR "Unable to drain serial transmitter.\n");
+
/* disable uart while changing speed */
bcm_uart_disable(port);
bcm_uart_flush(port);
--
1.9.3
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