Le 13/12/2016 à 17:27, Richard Genoud a écrit : > If we don't disable the transmitter in atmel_stop_tx, the DMA buffer > continues to send data until it is emptied. > This cause problems with the flow control (CTS is asserted and data are > still sent). > > So, disabling the transmitter in atmel_stop_tx is a sane thing to do. > > Tested on at91sam9g35-cm(DMA) > Tested for regressions on sama5d2-xplained(Fifo) and at91sam9g20ek(PDC) > > Cc: <stable@xxxxxxxxxxxxxxx> (beware, this won't apply before 4.3) > Signed-off-by: Richard Genoud <richard.genoud@xxxxxxxxx> > --- > drivers/tty/serial/atmel_serial.c | 11 +++++++++++ > 1 file changed, 11 insertions(+) > > NB: this is not for the 4.10 merge window, I'm just sending it now to > have some comments if someone is againts it. > > diff --git a/drivers/tty/serial/atmel_serial.c b/drivers/tty/serial/atmel_serial.c > index 168b10cad47b..f9d42de5ab2d 100644 > --- a/drivers/tty/serial/atmel_serial.c > +++ b/drivers/tty/serial/atmel_serial.c > @@ -481,6 +481,14 @@ static void atmel_stop_tx(struct uart_port *port) > /* disable PDC transmit */ > atmel_uart_writel(port, ATMEL_PDC_PTCR, ATMEL_PDC_TXTDIS); > } > + > + /* > + * Disable the transmitter. > + * This is mandatory when DMA is used, otherwise the DMA buffer > + * is fully transmitted. > + */ > + atmel_uart_writel(port, ATMEL_US_CR, ATMEL_US_TXDIS); > + > /* Disable interrupts */ > atmel_uart_writel(port, ATMEL_US_IDR, atmel_port->tx_done_mask); > > @@ -513,6 +521,9 @@ static void atmel_start_tx(struct uart_port *port) > > /* Enable interrupts */ > atmel_uart_writel(port, ATMEL_US_IER, atmel_port->tx_done_mask); > + > + /* re-enable the transmitter */ > + atmel_uart_writel(port, ATMEL_US_CR, ATMEL_US_TXEN); > } > > /* Hi Richard, I've just discovered that I have some weird behavior with this patch. On current Linus' tree, with sama5d2 + DMA, I see some garbage characters coming out of the console when I try to stop my system (reboot/halt) [1]. Moreover, and I do understand that it's not the problem right here, when applied on our linux-4.4-at91 branch (our vendor tree actually), it hangs the boot process as it seems that a burst of open/close of the serial port happens while starting the rootfs. It's definitively my own problem, but it can bring light to what we are seeing on Mainline... I think that we may need to flush the DMA channel in this atmel_stop_tx() function. Best regards, [1] If you want to test, you need to apply this patch for eMMC BTW: https://patchwork.kernel.org/patch/9617489/ -- Nicolas Ferre -- 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
