From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sergei Shtylyov Subject: Re: Disabling Command Completion Coalescing (CCC) in SATA AHCI Date: Fri, 20 May 2011 14:49:27 +0400 Message-ID: <4DD64737.10706@ru.mvista.com> References: Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: Received: from mail-bw0-f46.google.com ([209.85.214.46]:34182 "EHLO mail-bw0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934104Ab1ETKuQ (ORCPT ); Fri, 20 May 2011 06:50:16 -0400 Received: by bwz15 with SMTP id 15so2842699bwz.19 for ; Fri, 20 May 2011 03:50:15 -0700 (PDT) In-Reply-To: Sender: linux-ide-owner@vger.kernel.org List-Id: linux-ide@vger.kernel.org To: Pallav Bose Cc: linux-ide@vger.kernel.org Hello. On 20-05-2011 0:32, Pallav Bose wrote: > I'm working on 2.6.35.9 version of the Linux kernel and am trying to > disable Command Completion Coalescing. I have Native Command Queuing > enabled by activating the RAID mode through the BIOS. > I was looking at the Serial ATA AHCI 1.3 Specification and found on > page 115 that - > The CCC feature is only in use when CCC_CTL.EN is set to =911=92. If > CCC_CTL.EN is set to =910=92, no CCC interrupts shall be generated. > Next, I had a look at the relevant code (namely, the files concerning > AHCI) for this version of the kernel but wasn't able to make any > progress. I found the following enum constant - HOST_CAP_CCC =3D (1<< > 7) - in drivers/ata/ahci.h, but I'm not sure how this should be > modified to disable command coalescing. I did set HOST_CAP_CCC to 0 > but through some experiments that I conducted, I found that responses > were being batched. This constant is only used to report the controller capability, I s= ee no=20 other code depending on it, hence there doesn't seem to be any CCC supp= ort... [...] > The mass storage controller in the system is: Promise Technology, Inc= =2E > PDC20268 (Ultra100 TX2) (rev 02), I don't understand. This controller is not AHCI, and not even SATA = one. > and the HDD being used is: WD Caviar Black (Model number - WD1001FALS= ). WBR, Sergei