From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751402AbcDNBOd (ORCPT ); Wed, 13 Apr 2016 21:14:33 -0400 Received: from mail-pa0-f53.google.com ([209.85.220.53]:34109 "EHLO mail-pa0-f53.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750896AbcDNBOa (ORCPT ); Wed, 13 Apr 2016 21:14:30 -0400 Subject: Re: omap uart + dma issues (Re: [PATCH] tty: serial: 8250_omap: do not defer termios changes) To: Sekhar Nori , Sebastian Andrzej Siewior , John Ogness , Andy Shevchenko References: <8737r7ght7.fsf@linutronix.de> <570339E8.6010808@hurleysoftware.com> <87y48kftip.fsf@linutronix.de> <570BE48F.60801@hurleysoftware.com> <570BED7B.9080803@linutronix.de> <570C04C1.40201@hurleysoftware.com> <570D2A46.2050106@linutronix.de> <570D8C16.1010702@hurleysoftware.com> <570E295B.2030708@ti.com> Cc: Tony Lindgren , Greg Kroah-Hartman , linux-kernel@vger.kernel.org, linux-serial@vger.kernel.org, linux-omap@vger.kernel.org From: Peter Hurley Message-ID: <570EEEF0.2070102@hurleysoftware.com> Date: Wed, 13 Apr 2016 18:14:24 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.6.0 MIME-Version: 1.0 In-Reply-To: <570E295B.2030708@ti.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 04/13/2016 04:11 AM, Sekhar Nori wrote: > On Wednesday 13 April 2016 05:30 AM, Peter Hurley wrote: > >>>> - generates spurious uart interrupt for every rx dma transaction >>>> (ie., necessitates acking every UART interrupt, even UART_IIR_NO_INT) >>>> _Even with this workaround_, it still generates spurious interrupt warning >>>> which shuts off interrupts for several ms while logging the error >>>> message to the console, virtually guaranteeing lost data. >>> >>> as I wrote in my other email I think RDI should be disabled with DMA >> >> >> I'll test to see if disabling RDI eliminates the UART_IIR_NO_INT spurious >> interrupts. Ok; disabling UART_IER_RDI eliminates the UART_IIR_NO_INT spurious interrupts. However, disabling RDI disables RX timeout as well, so data just sits in the RX fifo with no way to get it out. AFAICT that's a showstopper. >>> according the Intel manual and I *think* someone here reported that >>> they see the same problem. >> >> Let's confirm with the Intel folks that this is true, which would argue >> for using the omap-style rx dma flow. > > Andy Shevchenko pointed this out here: https://lkml.org/lkml/2016/2/23/588 which Andy noted as well: On 02/23/2016 08:56 AM, Andy Shevchenko wrote: > The problem is that we have no separate bit to control timeout > interrupts from UART.