From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751616AbcBWMoC (ORCPT ); Tue, 23 Feb 2016 07:44:02 -0500 Received: from www.linutronix.de ([62.245.132.108]:39892 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751268AbcBWMn7 (ORCPT ); Tue, 23 Feb 2016 07:43:59 -0500 Subject: Re: [PATCH 0/4] serial: omap: robustify for high speed transfers To: Sekhar Nori , John Ogness , Tony Lindgren References: <87lh7hrjsg.fsf@linutronix.de> <56A66FCB.1000507@hurleysoftware.com> <87y4b85onp.fsf@linutronix.de> <56B15603.80807@hurleysoftware.com> <87wpqbihel.fsf@linutronix.de> <20160211210050.GY19432@atomide.com> <874md0yd81.fsf@linutronix.de> <56CC2D83.3090900@ti.com> Cc: Peter Hurley , gregkh@linuxfoundation.org, vinod.koul@intel.com, dan.j.williams@intel.com, peter.ujfalusi@ti.com, dmaengine@vger.kernel.org, linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org From: Sebastian Andrzej Siewior X-Enigmail-Draft-Status: N1110 Message-ID: <56CC5409.2050609@linutronix.de> Date: Tue, 23 Feb 2016 13:43:53 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Icedove/38.5.0 MIME-Version: 1.0 In-Reply-To: <56CC2D83.3090900@ti.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 8bit X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 02/23/2016 10:59 AM, Sekhar Nori wrote: >> With the am335x (Beaglebone Black, eDMA engine) I see 1000 DMA >> interrupts and 1000 spurious UART interrupts. The spurious UART >> interrupts arrive 30-50us _before_ the DMA interrupts. Always. >> >> If I disable UART timeout interrupts (RDI), the same test generates no >> spurious UART interrupts. Only 1000 DMA interrupts. > > To be clear, these interrupts are not caught as spurious by the > interrupt controller (INTC). They are detected by INTC as UART > interrupts. Just that you don't expect a timeout interrupt to happen at > the time you see the interrupt, correct? >>From what I remember the INTC says it is UART, correct. But UART's status register says "no interrupt" (IIR has UART_IIR_NO_INT set). So the UART driver returns IRQ_NONE which counts as spurious. It is just that once you disable RDI there are no more interrupts coming during DMA transfer. > Thanks, > Sekhar > Sebastian