From 0e5ec4140c4a8a38c4ff7293c018eb7da69a30db Mon Sep 17 00:00:00 2001 From: Russell Enderby Date: Tue, 5 Sep 2017 12:16:47 -0500 Subject: [PATCH] serial: bcm63xx: fix timing issue. MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit Issue where unprintable characters can occur or output is cut off over the serial uart / linux console depending on timing. 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. 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. Output before the fix: [0.306000] 14e00520.serial: ttyS0 at MMIO 0x14e00520 (irq = 9, base_baud = 1687500) is a° 0.315000] console[ttyS0] enabled Output verified after the 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 Signed-off-by: Greg Kroah-Hartman --- drivers/tty/serial/bcm63xx_uart.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/drivers/tty/serial/bcm63xx_uart.c b/drivers/tty/serial/bcm63xx_uart.c index 583c9a0c7ecc..8c48c3784831 100644 --- a/drivers/tty/serial/bcm63xx_uart.c +++ b/drivers/tty/serial/bcm63xx_uart.c @@ -507,9 +507,14 @@ 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); + /* disable uart while changing speed */ bcm_uart_disable(port); bcm_uart_flush(port); -- 2.20.1