From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tejun Heo Subject: Re: [PATCH 3/3] pata_amd: fix and improve cable detection Date: Sat, 03 Nov 2007 09:42:50 +0900 Message-ID: <472BC40A.3010205@gmail.com> References: <472B402A.4030009@gmail.com> <472B4078.90009@gmail.com> <472B40B0.6010702@gmail.com> <20071102154406.7596b384@the-village.bc.nu> <472BA318.7010406@gmail.com> <20071103001018.5a71bfd3@the-village.bc.nu> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: Received: from rv-out-0910.google.com ([209.85.198.184]:59217 "EHLO rv-out-0910.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756093AbXKCAnA (ORCPT ); Fri, 2 Nov 2007 20:43:00 -0400 Received: by rv-out-0910.google.com with SMTP id k20so931379rvb for ; Fri, 02 Nov 2007 17:42:59 -0700 (PDT) In-Reply-To: <20071103001018.5a71bfd3@the-village.bc.nu> Sender: linux-ide-owner@vger.kernel.org List-Id: linux-ide@vger.kernel.org To: Alan Cox Cc: Jeff Garzik , IDE/ATA development list Hello, again. Forgot one thing. Alan Cox wrote: >> all we can use is how the BIOS configured it. I suppose BIOS does it by >> issuing trial commands which I don't think adding to libata is a good idea. > > The BIOS does it by asking the hardware somehow. I traced one or two > BIOSes that far. The info is there but its not documented in the > slightest so only ACPI makes it visible via the BIOS. > >> Can you please lemme know what you don't like about the current >> implementation or what other approach you have in mind? I don't like >> Nvidia PATA either but there are a lot of people using it out there. > > We seem to be able to trust the drives and BIOS ACPI data for Nvidia (at > least what I have seen), so I guess we should simply declare the cable > type unknown, 80 wire if ACPI says it is and then do the drive detect > side ? The drive side can't be trusted. For the drive side detection work properly, there should be a capacitor attached to PDIAG-:CBLID- line so that the drive can tell 40C cable which connects CBLID- to the host connector by sampling while the capacitor is still discharging. If there's no capacitor on the line, 40C and 80C cables behave identically. Voltage rises as soon as CBLID- is disasserted and drive always reports 80C and that's what happens on my A8N-E. Hell of a way to save cost for one capacitor, I guess. :-( -- tejun