From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756985AbbAHTSJ (ORCPT ); Thu, 8 Jan 2015 14:18:09 -0500 Received: from gate.crashing.org ([63.228.1.57]:40189 "EHLO gate.crashing.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752722AbbAHTSH (ORCPT ); Thu, 8 Jan 2015 14:18:07 -0500 Message-ID: <1420744670.5830.44.camel@kernel.crashing.org> Subject: Re: [RFC] PPC: MPIC: necessary readback after EOI? From: Benjamin Herrenschmidt To: Scott Wood Cc: linuxppc-dev@lists.ozlabs.org, Purcareata Bogdan , linux-kernel@vger.kernel.org, Andreas Mohr Date: Thu, 08 Jan 2015 20:17:50 +0100 In-Reply-To: <1420650283.4961.52.camel@freescale.com> References: <20150105174616.GA3159@rhlx01.hs-esslingen.de> <1420481454.4961.16.camel@freescale.com> <1420641876.5830.32.camel@kernel.crashing.org> <1420650283.4961.52.camel@freescale.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.12.7-0ubuntu1 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2015-01-07 at 11:04 -0600, Scott Wood wrote: > On Wed, 2015-01-07 at 15:44 +0100, Benjamin Herrenschmidt wrote: > > On Mon, 2015-01-05 at 12:10 -0600, Scott Wood wrote: > > > It would have been nice if a code comment explained why it was doing the > > > readback... I don't see any particular need to wait for EOI completion > > > here (unlike when masking). > > > > The EOI is what causes the MPIC to drop it's EE output to the CPU, if the > > EOI is processed too slowly & asynchronously (posted write + 33Mhz MPIC) > > we observe cases of spurrious interrupts. We had some macs basically getting > > a spurrious irq for every MPIC interrupts... > > Shouldn't reading INTACK be what causes the MPIC to drop its EE output? Hrm, looks like I had too much wine or something, you are correct yes, it's the intack, so my explanation is bogus. So we are down to possibly delaying the raising back of the CPU priority which is not a big deal indeed, we could probably get rid of the read back. Ben.