From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261188AbTLCUpM (ORCPT ); Wed, 3 Dec 2003 15:45:12 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261569AbTLCUpL (ORCPT ); Wed, 3 Dec 2003 15:45:11 -0500 Received: from havoc.gtf.org ([63.247.75.124]:37808 "EHLO havoc.gtf.org") by vger.kernel.org with ESMTP id S261188AbTLCUor (ORCPT ); Wed, 3 Dec 2003 15:44:47 -0500 Date: Wed, 3 Dec 2003 15:44:46 -0500 From: Jeff Garzik To: linux-kernel@vger.kernel.org, linux-ide@vger.kernel.org, linux-scsi@vger.kernel.org Subject: Serial ATA (SATA) for Linux status report Message-ID: <20031203204445.GA26987@gtf.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.3.28i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Editor's preface: This is clearly a first draft, only covering the basics. In order for this document to be effective, I request that users and developers send me (or post) their SATA driver questions and issues. I will do my best to address them here. Serial ATA (SATA) for Linux status report Dec 3, 2003 Hardware support ================ Intel ICH5 ---------- Summary: No TCQ. Looks like a PATA controller, but with a few added, non-standard SATA port controls. libata driver status: Production, but see issue #2, #3. drivers/ide driver status: Production, but see issue #1, #2. Issue #1: Depending on BIOS settings, IDE driver may lock up computer when probing drives. Issue #2: Excessive interrupts are seen in some configurations. Issue #3: "Enhanced mode" or "SATA-only mode" may need to be set in BIOS. Intel ICH6 ("AHCI") ------------------- Summary: Per-device queues, full SATA control including hotplug and PM. libata driver status: In development. Promise ------- Summary: Per-host queues on all controllers. Full SATA control including hotplug and PM on all but one controller. libata driver status: Beta. Silicon Image 3112 ------------------ Summary: No TCQ. Looks like a PATA controller, but with full SATA control including hotplug and PM. libata driver status: Alpha. drivers/ide driver status: Production, but see issue #4. Issue #4: Need to have the most recent fixes posted to lkml, for stable operation and full performance (where possible). Broadcom/ServerWorks/Apple -------------------------- Summary: Huge per-device queues, full SATA control including hotplug and PM. libata driver status: Beta. VIA --- Summary: No TCQ. Looks like a PATA controller, but with full SATA control including hotplug and PM. libata driver status: Beta. Software support ================ Basic Serial ATA support ------------------------ The "ATA host state machine", the core of the entire driver, is considered production-stable. The error handling is _very_ simple, but at this stage that is an advantage. Error handling code anywhere is inevitably both complex and sorely under-tested. libata error handling is intentionally simple. Positives: Easy to review and verify correctness. Never data corruption. Negatives: if an error occurs, libata will simply send the error back the block layer. There are limited retries by the block layer, depending on the type of error, but there is never a bus reset. Or in other words: "it's better to stop talking to the disk than compound existing problems with further problems." As Serial ATA matures, and host- and device-side errata become apparent, the error handling will be slowly refined. I am planning to work with a few (kind!) disk vendors, to obtain special drives/firmwares that allow me to inject faults, and otherwise exercise error handling code. Queueing support ---------------- Even though some SATA host controllers on the market already support command queueing (a.k.a. "TCQ"), libata does not yet support it. However, libata was designed from the ground-up to support queueing, so I need only change a few lines of code, and write two functions, to enable this behavior. Queueing will be enabled in libata soon, but to do so requires a long stretch of testing on a large variety of controllers and drives. This is very time-intensive, and is the largest part of this task. Tangent: Host-based queueing and Native Command Queueing Queueing is the process of sending multiple commands to a single device, without waiting for prior commands to finish. This increases performance and reduces latency. There are three types of queueing in the ATA world: 1) "legacy TCQ" -- some PATA devices support this. Just ignore it, it's going away. 2) "host-based TCQ" -- the host controller supports a queue of drive commands, whether or not the drive supports it. 3) "Native Command Queueing" -- both host and drive cooperate in the queueing and execution of drive commands. This should provide the highest performance and lowest latency of all three options. #1 is support by drivers/ide _only_. libata will not support this. #2 will soon be supported by libata. #3 will be supported by libata when hardware is available from drive manufacturers. Hotplug support --------------- All SATA is hotplug. libata does not support hotplug... yet. Power Management support ------------------------ Over and above the power management specified in the ATA/ATAPI specification, one can aggressively control the power consumption of SATA hosts, the SATA bus, and the SATA device.