linux-kernel - Re: [patch 067/104] libata: improve phantom device detection

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Date:	Thu, 04 Dec 2008 13:20:15 +0900
From:	Tejun Heo <tj@...nel.org>
To:	Greg KH <gregkh@...e.de>
CC:	linux-kernel@...r.kernel.org, stable@...nel.org,
	Justin Forbes <jmforbes@...uxtx.org>,
	Zwane Mwaikambo <zwane@....linux.org.uk>,
	"Theodore Ts'o" <tytso@....edu>,
	Randy Dunlap <rdunlap@...otime.net>,
	Dave Jones <davej@...hat.com>,
	Chuck Wolber <chuckw@...ntumlinux.com>,
	Chris Wedgwood <reviews@...cw.f00f.org>,
	Michael Krufky <mkrufky@...uxtv.org>,
	Chuck Ebbert <cebbert@...hat.com>,
	Domenico Andreoli <cavokz@...il.com>, Willy Tarreau <w@....eu>,
	Rodrigo Rubira Branco <rbranco@...checkpoint.com>,
	Jake Edge <jake@....net>, Eugene Teo <eteo@...hat.com>,
	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	alan@...rguk.ukuu.org.uk, Jeff Garzik <jgarzik@...hat.com>
Subject: Re: [patch 067/104] libata: improve phantom device detection

> 2.6.27-stable review patch.  If anyone has any objections, please let us know.
> 
> ------------------
> From: Tejun Heo <tj@...nel.org>
> 
> commit 6a6b97d360702b98c02c7fca4c4e088dcf3a2985 upstream.
> 
> Currently libata uses four methods to detect device presence.
> 
> 1. PHY status if available.
> 2. TF register R/W test (only promotes presence, never demotes)
> 3. device signature after reset
> 4. IDENTIFY failure detection in SFF state machine
> 
> Combination of the above works well in most cases but recently there
> have been a few reports where a phantom device causes unnecessary
> delay during probe.  In both cases, PHY status wasn't available.  In
> one case, it passed #2 and #3 and failed IDENTIFY with ATA_ERR which
> didn't qualify as #4.  The other failed #2 but as it passed #3 and #4,
> it still caused failure.
> 
> In both cases, phantom device reported diagnostic failure, so these
> cases can be safely worked around by considering any !ATA_DRQ IDENTIFY
> failure as NODEV_HINT if diagnostic failure is set.
> 
> Signed-off-by: Tejun Heo <tj@...nel.org>
> Signed-off-by: Jeff Garzik <jgarzik@...hat.com>
> Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

Alan thinks this patch could cause regression.  Given that we're
nearing the end of 2.6.28-rc cycles, I don't think it's critical to
include this into 2.6.27-stable or at least it can wait a bit more.

Thanks.

-- 
tejun
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