Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753491AbdCONho (ORCPT ); Wed, 15 Mar 2017 09:37:44 -0400 Received: from mail-ot0-f195.google.com ([74.125.82.195]:32815 "EHLO mail-ot0-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753448AbdCONgt (ORCPT ); Wed, 15 Mar 2017 09:36:49 -0400 MIME-Version: 1.0 In-Reply-To: References: <20161213162756.16139-1-richard.genoud@gmail.com> From: Richard Genoud Date: Wed, 15 Mar 2017 14:36:27 +0100 Message-ID: Subject: Re: [PATCH] tty/serial: atmel_serial: BUG: stop DMA from transmitting in stop_tx To: Nicolas Ferre Cc: Alexandre Belloni , Cyrille Pitchen , "linux-arm-kernel@lists.infradead.org" , Greg Kroah-Hartman , "linux-serial@vger.kernel.org" , "linux-kernel@vger.kernel.org" Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: 8bit X-MIME-Autoconverted: from quoted-printable to 8bit by mail.home.local id v2FDc3YL019783 Content-Length: 3039 Lines: 85 2017-03-15 12:37 GMT+01:00 Nicolas Ferre : > 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: (beware, this won't apply before 4.3) >> Signed-off-by: Richard Genoud >> --- >> 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.