From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tejun Heo Subject: Re: questions regarding possible violation of AHCI spec in AHCI driver Date: Wed, 08 Dec 2010 19:52:27 +0100 Message-ID: <4CFFD3EB.10800@kernel.org> References: <4CFEE569.4030204@gmail.com> <4CFF58D2.4040006@kernel.org> ,<4CFFCD56.6050608@kernel.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: Received: from hera.kernel.org ([140.211.167.34]:37739 "EHLO hera.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754912Ab0LHSw7 (ORCPT ); Wed, 8 Dec 2010 13:52:59 -0500 In-Reply-To: Sender: linux-ide-owner@vger.kernel.org List-Id: linux-ide@vger.kernel.org To: Jian Peng Cc: Robert Hancock , "linux-kernel@vger.kernel.org" , "jgarzik@pobox.com" , ide Hello, On 12/08/2010 07:48 PM, Jian Peng wrote: > So it is reasonable to add extra check in ahci_start_engine() without returning status of ST bit. If so, here is my patch > > --- libahci.c.orig 2010-12-08 10:42:48.383976763 -0800 > +++ libahci.c 2010-12-08 10:45:17.495156944 -0800 > @@ -542,6 +542,13 @@ > { > void __iomem *port_mmio = ahci_port_base(ap); > u32 tmp; > + u8 status = readl(port_mmio + PORT_TFDATA) & 0xFF; > + > + /* avoid race condition per spec (end of section 10.1.2) */ > + if (status & (ATA_BUSY | ATA_DRQ) || > + ahci_scr_read(&ap->link, SCR_STATUS, &tmp) || > + (tmp & 0x0f) != 0x03) > + return; > > /* start DMA */ > tmp = readl(port_mmio + PORT_CMD); Yes, it is reasonable but I want to see that it actually fixes something. There are just too many controllers which use this path to blindly apply the above change and given my previous explanation even without the above change any ahci controller _should_ work fine. Thanks. -- tejun