From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jeff Garzik Subject: Re: Help with SATA driver/libata/SCSI subsystem Date: Wed, 13 May 2009 15:36:31 -0400 Message-ID: <4A0B213F.2060900@garzik.org> References: Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from srv5.dvmed.net ([207.36.208.214]:57298 "EHLO mail.dvmed.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751331AbZEMTgd (ORCPT ); Wed, 13 May 2009 15:36:33 -0400 In-Reply-To: Sender: linux-ide-owner@vger.kernel.org List-Id: linux-ide@vger.kernel.org To: C Z Cc: linux-kernel@vger.kernel.org, Linux IDE mailing list C Z wrote: > I am attempting to write a SATA driver under libata for a custom core on a Microblaze Xilinx FPGA. I can not get ata_device_add() in drivers/ata/libata-core.c to return successfully. > > I have tracked the immediate problem to the function scsi_eh_flush_done_q() in drivers/scsi/scsi_error.c. The problem is this function calls "list_for_each_entry_safe(scmd, next, done_q, eh_entry)". Unfortunately, this returns the result scmd = 0xFFFFFFF0. This very strange address is the result of containerof() being called on a NULL pointer. The NULL pointer is the done_q list head. This is clearly wrong. > > I have 2 questions. First, why is libata invoking the error handler after a probe in ata_device_add? This seems very counter intuitive to me. It isn't at all clear why libata needs to do this. Can someone explain the rationale behind this function? > > Second, and more importantly, can someone who is experienced with this subsystem explain in simple terms the call flow that happens in the function ata_device_add? I am having trouble understanding which procedure should have issued a command and set up the done_q list head. Therefore I don't know how to track this problem further. Indeed, it doesn't appear to me that anyone actually issues a command during the probe. I'm guessing it was supposed to have been done somewhere, but where/in what function should I start looking? What was the command supposed to have been? > > I am using an old kernel version 2.6.20, however I don't believe these subsystems have changed substantially since then. > > Any assistance or advice from someone who has dealth with this area of the kernel before is appreciated. Please cc linux-ide@vger.kernel.org, and turn on word wrapping in your email. Please also use an updated kernel, libata has changed substantially since 2.6.20. Hardware drivers do not invoke ata_device_add() [which does not exist anymore], so it sounds like you are doing something really wrong... Jeff