linux-kernel - Re: [PATCH] Re: [git patches] libata updates - (improve post-reset device ready test) regression

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Message-ID: <482541E3.6020001@gmail.com>
Date:	Sat, 10 May 2008 15:34:11 +0900
From:	Tejun Heo <htejun@...il.com>
To:	Jeff Garzik <jeff@...zik.org>
CC:	Markus Trippelsdorf <markus@...ppelsdorf.de>,
	linux-ide@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Takashi Iwai <tiwai@...e.de>, marc.c.dionne@...il.com,
	dl9pf@....de, bug-track@...her-privat.net, sitsofe@...oo.com
Subject: Re: [PATCH] Re: [git patches] libata updates - (improve post-reset
 device ready test) regression

Jeff Garzik wrote:
> Tejun Heo wrote:
>> This means that we need to make custom readiness tests for controllers 
>> using 0x77 or 0x7f.  Eeeek... Both groups of controllers are behaving 
>> in incorrect way.  Controllers shouldn't use 0x77 or 0x7f for either 
>> busy or ready states - it's invalid for both, yet, some use the 77/7f 
>> for busy while others use them for ready state.  Great.  :-(
> 
> I think that's assuming too much?  PATA and SATA are quite different 
> here... in PATA the status is mostly the value from the device directly 
> off the wires.  in SATA, it may be from the device or from the 
> controller.  And "smart" or firmware-based controllers may generate 
> their own status, too, apart from the device's status.
 >
> So that results in varied status returns, and not all the time is a 
> definite "ready" or "not ready" obvious.

I think it's pretty safe to say that these weird ready values are from 
TF emulation on controller side.  The ready/not ready distinction is 
probably too simplistic but those values aren't supposed to appear 
during post-reset readiness test.

Sorry about the big regression.  Heh... It's amazing how all the 
controllers I tested didn't show the problem and I did test a good 
number of combinations.

I still think it would be better to have a unified readiness test 
function.  The problem is subtle (device misdetection on hotplug of 
certain drives) and went unnoticed quite some time for JMB ahcis && test 
coverage over those things can't be good.  I'll try to think about 
something better.

Thanks.

-- 
tejun
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