2017-03-15 12:37 GMT+01:00 Nicolas Ferre <nicolas.ferre@xxxxxxxxx>: > 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, Hi ! > > 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]. Yes, I've also seen that on my board, it was on my todo list. (Although I didn't know this patch was the culprit !) > > 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... aïe ! This is clearly something we'll have to understand ! > I think that we may need to flush the DMA channel in this > atmel_stop_tx() function. > yes, I'll look into that. > 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 Thanks ! Richard. -- 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
