From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753620AbdCORGX (ORCPT ); Wed, 15 Mar 2017 13:06:23 -0400 Received: from esa4.microchip.iphmx.com ([68.232.154.123]:18980 "EHLO esa4.microchip.iphmx.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752736AbdCORFd (ORCPT ); Wed, 15 Mar 2017 13:05:33 -0400 X-Greylist: delayed 579 seconds by postgrey-1.27 at vger.kernel.org; Wed, 15 Mar 2017 13:05:33 EDT X-IronPort-AV: E=Sophos;i="5.36,169,1486450800"; d="scan'208";a="237825" Subject: Re: [RFC PATCH] tty/serial: atmel: fix TX path in atmel_console_write() To: Richard Genoud , References: <20170315152948.10978-1-nicolas.ferre@microchip.com> <074d057e-4971-a325-e985-3f5046536225@gmail.com> CC: , , "stable # 4 . 4+" From: Nicolas Ferre Organization: microchip Message-ID: Date: Wed, 15 Mar 2017 17:56:11 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.7.0 MIME-Version: 1.0 In-Reply-To: <074d057e-4971-a325-e985-3f5046536225@gmail.com> Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Le 15/03/2017 à 17:19, Richard Genoud a écrit : > On 15/03/2017 16:29, Nicolas Ferre wrote: >> A side effect of 89d8232411a8 ("tty/serial: atmel_serial: BUG: stop DMA >> from transmitting in stop_tx") is that the console can be called with >> TX path disabled. Then the system would hang trying to push charecters >> out in atmel_console_putchar(). >> >> Signed-off-by: Nicolas Ferre >> Fixes: 89d8232411a8 ("tty/serial: atmel_serial: BUG: stop DMA from transmitting >> in stop_tx") >> Cc: stable # 4.4+ >> --- >> Hi Richard, >> >> I found this to fix the problem with system hang in my linux-4.4-at91 branch >> (in the atmel_console_putchar() waiting loop actually). I'm open to more >> insignt. >> As we cannot figure out if this bit is set or not, I didn't preserve the >> current status... >> >> Regards, > > So, I'm guessing that you may see some lines/characters printed twice on > the screen, don't you ? Well, actually, I don't think so because the repetitions that I see are probably due to open/close/open/close/re-open/... of the serial console itself. Same with the line "random: udevd: uninitialized urandom read (16 bytes read, 21 bits of entropy available)", they happen at different moment in time => the printk log timestamping seem to indicate that they are different. Here is my log: http://code.bulix.org/bok23n-123056 Regards, >> drivers/tty/serial/atmel_serial.c | 3 +++ >> 1 file changed, 3 insertions(+) >> >> diff --git a/drivers/tty/serial/atmel_serial.c b/drivers/tty/serial/atmel_serial.c >> index dcebb28ffbc4..7372dbdb7a4c 100644 >> --- a/drivers/tty/serial/atmel_serial.c >> +++ b/drivers/tty/serial/atmel_serial.c >> @@ -2483,6 +2483,9 @@ static void atmel_console_write(struct console *co, const char *s, u_int count) >> pdc_tx = atmel_uart_readl(port, ATMEL_PDC_PTSR) & ATMEL_PDC_TXTEN; >> atmel_uart_writel(port, ATMEL_PDC_PTCR, ATMEL_PDC_TXTDIS); >> >> + /* Make sure that tx path is actually able to send characters */ >> + atmel_uart_writel(port, ATMEL_US_CR, ATMEL_US_TXEN); >> + >> uart_console_write(port, s, count, atmel_console_putchar); >> >> /* >> > > Richard. > -- Nicolas Ferre