Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752159AbdHLWIA (ORCPT ); Sat, 12 Aug 2017 18:08:00 -0400 Received: from mail.pqgruber.com ([178.189.19.235]:31155 "EHLO mail.pqgruber.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752018AbdHLWH7 (ORCPT ); Sat, 12 Aug 2017 18:07:59 -0400 Date: Sun, 13 Aug 2017 00:07:56 +0200 From: Clemens Gruber To: Uwe =?iso-8859-1?Q?Kleine-K=F6nig?= Cc: linux-serial@vger.kernel.org, Greg Kroah-Hartman , Fabio Estevam , linux-kernel@vger.kernel.org, Ian Jamison Subject: Re: [PATCH] serial: imx: Improve PIO prevention if TX DMA has been started Message-ID: <20170812220755.GA22225@archie.localdomain> References: <20170812151210.10420-1-clemens.gruber@pqgruber.com> <20170812195451.2g65wifawouz4t7d@pengutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20170812195451.2g65wifawouz4t7d@pengutronix.de> User-Agent: Mutt/1.8.3 (2017-05-23) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2138 Lines: 55 On Sat, Aug 12, 2017 at 09:54:51PM +0200, Uwe Kleine-K?nig wrote: > On Sat, Aug 12, 2017 at 05:12:10PM +0200, Clemens Gruber wrote: > > The imx_transmit_buffer function should return if TX DMA has already > > been started and not just skip over the buffer PIO write loop. (Which > > did fix the initial problem, but could have unintentional side-effects) > > > > Tested on an i.MX6Q board with half-duplex RS-485 and with RS-232. > > > > Cc: Ian Jamison > > Cc: Uwe-Kleine K?nig > > Fixes: 514ab34dbad6 ("serial: imx: Prevent TX buffer PIO write when a > > DMA has been started") > > AFAIK no newline in the Fixes: line. Thanks. A checkpatch warning for this would be great. > > > Signed-off-by: Clemens Gruber > > --- > > drivers/tty/serial/imx.c | 3 ++- > > 1 file changed, 2 insertions(+), 1 deletion(-) > > > > diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c > > index 80934e7bd67f..fce538eb8c77 100644 > > --- a/drivers/tty/serial/imx.c > > +++ b/drivers/tty/serial/imx.c > > @@ -452,13 +452,14 @@ static inline void imx_transmit_buffer(struct imx_port *sport) > > if (sport->dma_is_txing) { > > temp |= UCR1_TDMAEN; > > writel(temp, sport->port.membase + UCR1); > > + return; > > } else { > > writel(temp, sport->port.membase + UCR1); > > imx_dma_tx(sport); > > } > > Shouldn't the return go here? Yes, it can also go here (and probably should). The problem of xmit->tail jumping over xmit->head occurs only if we are already DMA txing and then go into the PIO loop, but not the first time after calling imx_dma_tx. That's why the v1 passed the tests too. I'll have to conduct a few more tests and if they succeed I'll send a v2 where we return in both cases (already txing and starting to). > Did you understand the problem? Can you say why this only hurts in RS485 > half-duplex but not (as it seems) in regular rs232 mode? I am not sure anyone understands (yet) why it a) only hurts RS-485 and b) only occurs on SMP systems. If you have more insight, please share it. :) Cheers, Clemens