From: Stefan Agner <stefan.ag...@toradex.com> After overruns the FIFO pointers become misaligned. This typically shows by characters still being stuck in the FIFO despite the empty flag being asserted. After the first assertion of the overrun flag the empty flag still seems to indicate FIFO state correctly and all data can be read. However, after another overrun assertion the FIFO seems to be off by one such that the last received character is still in the FIFO (despite the empty flag being asserted).
Flushing the receive FIFO reinitializes pointers. Hence it is recommended to flush the FIFO after overruns, see also: https://community.nxp.com/thread/321175 Hence, on assertion of the overrun flag read the remaining data from the FIFO and flush buffers. Signed-off-by: Stefan Agner <stefan.ag...@toradex.com> Acked-by: Max Krummenacher <max.krummenac...@toradex.com> Cc: Stefan Agner <ste...@agner.ch> Cc: Chris Healy <cphe...@gmail.com> Cc: Cory Tusar <cory.tu...@zii.aero> Cc: Lucas Stach <l.st...@pengutronix.de> Cc: Greg Kroah-Hartman <gre...@linuxfoundation.org> Cc: Jiri Slaby <jsl...@suse.com> Cc: linux-...@nxp.com Cc: linux-ser...@vger.kernel.org Cc: linux-kernel@vger.kernel.org --- drivers/tty/serial/fsl_lpuart.c | 15 +++++++++++++-- 1 file changed, 13 insertions(+), 2 deletions(-) diff --git a/drivers/tty/serial/fsl_lpuart.c b/drivers/tty/serial/fsl_lpuart.c index 0643fa368d35..317bbc1dd2b4 100644 --- a/drivers/tty/serial/fsl_lpuart.c +++ b/drivers/tty/serial/fsl_lpuart.c @@ -799,7 +799,7 @@ static irqreturn_t lpuart_txint(int irq, void *dev_id) static irqreturn_t lpuart_rxint(int irq, void *dev_id) { struct lpuart_port *sport = dev_id; - unsigned int flg, ignored = 0; + unsigned int flg, ignored = 0, overrun = 0; struct tty_port *port = &sport->port.state->port; unsigned long flags; unsigned char rx, sr; @@ -826,7 +826,7 @@ static irqreturn_t lpuart_rxint(int irq, void *dev_id) sport->port.icount.frame++; if (sr & UARTSR1_OR) - sport->port.icount.overrun++; + overrun++; if (sr & sport->port.ignore_status_mask) { if (++ignored > 100) @@ -853,6 +853,17 @@ static irqreturn_t lpuart_rxint(int irq, void *dev_id) } out: + if (overrun) { + sport->port.icount.overrun += overrun; + + /* + * Overruns cause FIFO pointers to become missaligned. + * Flushing the receive FIFO reinitializes the pointers. + */ + writeb(UARTCFIFO_RXFLUSH, sport->port.membase + UARTCFIFO); + writeb(UARTSFIFO_RXOF, sport->port.membase + UARTSFIFO); + } + spin_unlock_irqrestore(&sport->port.lock, flags); tty_flip_buffer_push(port); -- 2.21.0
