When the pl011 is being used for a console, pl011_console_write forces the control register (CR) to enable the UART for transmission and then restores this to the original value afterwards. It does this while holding the port lock. Unfortunately, when the uart is started or shutdown - say in response to userland using the serial device for a terminal - then this updates the control register without any locking. This means we can have pl011_console_write Save CR pl011_startup Initialise CR, e.g. enable receive pl011_console_write Restore old CR with receive not enabled this result is a serial port which doesn't respond to any input. A similar race in reverse could happen when the device is shutdown. We can fix these problems by taking the port lock when updating CR. Signed-off-by: Jon Medhurst <tixy@xxxxxxxxxx> --- I can't help but think I've missed something fundamental here as it seems wrong to be in the situation at all where were initialising hardware if it is already being used? Also, even with this fix I still see spurious/corrupt output on the serial port at the point the port is initialised, so there is obviously some other issues in this area. drivers/tty/serial/amba-pl011.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c index 7203864..a0dfb86 100644 --- a/drivers/tty/serial/amba-pl011.c +++ b/drivers/tty/serial/amba-pl011.c @@ -1537,6 +1537,8 @@ static int pl011_startup(struct uart_port *port) /* * Provoke TX FIFO interrupt into asserting. */ + spin_lock_irq(&uap->port.lock); + cr = UART01x_CR_UARTEN | UART011_CR_TXE | UART011_CR_LBE; writew(cr, uap->port.membase + UART011_CR); writew(0, uap->port.membase + UART011_FBRD); @@ -1561,6 +1563,8 @@ static int pl011_startup(struct uart_port *port) cr |= UART01x_CR_UARTEN | UART011_CR_RXE | UART011_CR_TXE; writew(cr, uap->port.membase + UART011_CR); + spin_unlock_irq(&uap->port.lock); + /* * initialise the old status of the modem signals */ @@ -1629,11 +1633,13 @@ static void pl011_shutdown(struct uart_port *port) * it during startup(). */ uap->autorts = false; + spin_lock_irq(&uap->port.lock); cr = readw(uap->port.membase + UART011_CR); uap->old_cr = cr; cr &= UART011_CR_RTS | UART011_CR_DTR; cr |= UART01x_CR_UARTEN | UART011_CR_TXE; writew(cr, uap->port.membase + UART011_CR); + spin_unlock_irq(&uap->port.lock); /* * disable break condition and fifos -- 1.7.10.4 -- To unsubscribe from this list: send the line "unsubscribe linux-serial" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
