The CREAD feature of termios is implemented by setting/clearing UART_LSR_DR within @ignore_status_mask. For this feature to function correctly, it requires that UART_LSR_DR is never masked (unset) in @read_status_mask so that uart_insert_char() can properly drop the character if CREAD is disabled. Currently there are code paths that clear/set UART_LSR_DR from @read_status_mask at times. This appears to be a relic from Linux 1.1.60, where @read_status_mask could be used to mask all UART_LSR reading. However, since Linux 2.1.8 that is no longer the case. Now if UART_LSR_DR is cleared from @read_status_mask, received characters may not be dropped even though CREAD is disabled. This can be seen when: - CREAD is disabled (UART_LSR_DR is set in @ignore_status_mask) - LSR has an error bit set from UART_LSR_BRK_ERROR_BITS (and that error is not ignored via @ignore_status_mask) - UART_LSR_DR is cleared in @read_status_mask In this case characters will be inserted into the tty buffer even though they should be ignored. Remove all setting/clearing of UART_LSR_DR for @read_status_mask except for its initialization. Signed-off-by: John Ogness <john.ogness@xxxxxxxxxxxxx> --- drivers/tty/serial/8250/8250_core.c | 1 - drivers/tty/serial/8250/8250_omap.c | 1 - drivers/tty/serial/8250/8250_port.c | 1 - 3 files changed, 3 deletions(-) diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c index 5f9f06911795..2b70e82dffeb 100644 --- a/drivers/tty/serial/8250/8250_core.c +++ b/drivers/tty/serial/8250/8250_core.c @@ -675,7 +675,6 @@ static void serial_8250_overrun_backoff_work(struct work_struct *work) uart_port_lock_irqsave(port, &flags); up->ier |= UART_IER_RLSI | UART_IER_RDI; - up->port.read_status_mask |= UART_LSR_DR; serial_out(up, UART_IER, up->ier); uart_port_unlock_irqrestore(port, flags); } diff --git a/drivers/tty/serial/8250/8250_omap.c b/drivers/tty/serial/8250/8250_omap.c index 5290aed76a5e..10144fcc0363 100644 --- a/drivers/tty/serial/8250/8250_omap.c +++ b/drivers/tty/serial/8250/8250_omap.c @@ -838,7 +838,6 @@ static void omap_8250_unthrottle(struct uart_port *port) if (up->dma) up->dma->rx_dma(up); up->ier |= UART_IER_RLSI | UART_IER_RDI; - port->read_status_mask |= UART_LSR_DR; serial_out(up, UART_IER, up->ier); uart_port_unlock_irqrestore(port, flags); diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c index a5c1b069c67b..3b9dc2bb06eb 100644 --- a/drivers/tty/serial/8250/8250_port.c +++ b/drivers/tty/serial/8250/8250_port.c @@ -1390,7 +1390,6 @@ static void serial8250_stop_rx(struct uart_port *port) serial8250_rpm_get(up); up->ier &= ~(UART_IER_RLSI | UART_IER_RDI); - up->port.read_status_mask &= ~UART_LSR_DR; serial_port_out(port, UART_IER, up->ier); serial8250_rpm_put(up); -- 2.39.5
