From mboxrd@z Thu Jan 1 00:00:00 1970 From: Benjamin Herrenschmidt Subject: Re: [PATCH] SCSI midlayer power management Date: Thu, 12 Aug 2004 09:36:40 +1000 Sender: linux-kernel-owner@vger.kernel.org Message-ID: <1092267400.2136.24.camel@gaston> References: <4119611D.60401@optonline.net> <20040811080935.GA26098@elf.ucw.cz> <411A1B72.1010302@optonline.net> <1092231462.2087.3.camel@mulgrave> Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1092231462.2087.3.camel@mulgrave> To: James Bottomley Cc: Nathan Bryant , Pavel Machek , Linux SCSI Reflector , Linux Kernel list , Jeff Garzik List-Id: linux-scsi@vger.kernel.org > Actually, the answer is to most intents and purposes "yes". You are > technically correct: there's no way to disable DMA in SCSI. However, > once a device is quiesced, it has no outstanding commands, so there will > be no outstanding DMA to that device. When all devices on a host have > been quiesced, then there will be no DMA at all going on *except* if the > user initiates any via another interface (like sending a device probe or > doing a unit scan). The guarantee should be strong enough for swsusp to > proceed, but we can look at quiescing a host properly (however, we'd > need to move to a better host state model than we currently possess). Some hosts will continuously DMA to memory iirc.. I remember having a problem with 53c8xx on some macs when transitionning from MacOS to Linux because of that. We need to properly quisce the host, but that's a per host driver thing and shouldn't be too difficult. Regarding suspend-to-disk, it's fairly easy for the sd driver not to spin down the disk for S4 (only for S3). However, we will still probably do at least a bus reset when waking up... Pavel: That's one of the reason I wanted an argument to resume() too so drivers can make a difference between the immediate wakeup that happens for writing the image to disk, vs. the real wakeup on resume. In the first case, SCSI can avoid the bus reset, and any kind of re-configuring, in the second case, the full stuff might be necessary. Ben.