From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tejun Heo Subject: Re: [ANNOUNCE] libata EH/NCQ/hotplug/PM git tree Date: Sat, 13 May 2006 19:20:36 +0900 Message-ID: <4465B2F4.3040208@gmail.com> References: <44614592.7080301@gmail.com> <446536C5.80503@pobox.com> <44653807.3030101@gmail.com> <44655496.9030402@pobox.com> <44655986.3060007@gmail.com> <4465AEC0.30300@stesmi.com> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from wr-out-0506.google.com ([64.233.184.239]:28251 "EHLO wr-out-0506.google.com") by vger.kernel.org with ESMTP id S932100AbWEMKUp (ORCPT ); Sat, 13 May 2006 06:20:45 -0400 Received: by wr-out-0506.google.com with SMTP id i22so665964wra for ; Sat, 13 May 2006 03:20:44 -0700 (PDT) In-Reply-To: <4465AEC0.30300@stesmi.com> Sender: linux-ide-owner@vger.kernel.org List-Id: linux-ide@vger.kernel.org To: Stefan Smietanowski Cc: Jeff Garzik , Alan Cox , Albert Lee , Jens Axboe , Edward Falk , Carlos Pardo , Raymond Liu , "linux-ide@vger.kernel.org" Stefan Smietanowski wrote: >> Which is understandable considering AHCI doesn't construct FISes itself. >> I don't think PM requires more hardware support than being capable for >> setting PMP in the FISes, which AHCI certainly can (standing down on >> collision for SDB notify aside). I can give it a shot but it clearly >> violates the spec, and even if it works, we would need to print big fat >> warning message while attaching PM. >> > > Are you saying that the next big thing since sliced bread (AHCI) that's > supposed to unite the world and make everybody sing Kumbayah doesn't > support port multipliers (according to the spec) ? > > Or am I totally misreading this. Heh heh. I love AHCI too, but as far as PMS is concerned, AHCI is not saving any world. There's a bit called SPM (supports Port Multiplier) in the capability register. If the bit is set, AHCI support PM by command-based switching, which ummm... sucks - only one device can have active commands at any given time. AHCI v1.1 (the current spec) lists FIS-based switching PMS as 'to be specified in a future AHCI specification'. To make matters worse, not many AHCI controllers seem to have that bit set. My ICH7R (P5LD2) doesn't and I would be surprised if any of ICH6R/M and ICH7M have that bit set. Zhao reported that ESB2 (server chipset w/ 6 SATA ports) have that bit set, so there are some controllers supporting PM out there. However, cmd-switching PMS doesn't require much support from HBA, and I don't see why my ICH7R cannot do PMS. I'm currently giving it a try now. So, ATM, if you want PMS, sil3124/3132 series is the best choice. -- tejun