linux-kernel - Re: [smartmontools-support] inactive SATA drives won't stay in standby or sleep, PATA models did. (fwd)

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Message-ID: <18685.35827.914278.413151@harpo.it.uu.se>
Date:	Tue, 21 Oct 2008 09:59:47 +0200
From:	Mikael Pettersson <mikpe@...uu.se>
To:	Mikael Pettersson <mikpe@...uu.se>
Cc:	Tejun Heo <htejun@...il.com>,
	Christian Mueller <Christian.Mueller@....com>,
	Bruce Allen <ballen@...vity.phys.uwm.edu>,
	Smartmontools Mailing List 
	<smartmontools-support@...ts.sourceforge.net>,
	LKML <linux-kernel@...r.kernel.org>,
	IDE/ATA development list <linux-ide@...r.kernel.org>
Subject: Re: [smartmontools-support] inactive SATA drives won't stay in standby
 or sleep, PATA models did. (fwd)

On Mon, 20 Oct 2008 01:40:21 +0200, Mikael Pettersson wrote:
>On Mon, 13 Oct 2008 14:16:24 +0900, Tejun Heo wrote:
>>Mikael Pettersson wrote:
>>> - hardreset in sata_promise seems broken. I'll take a closer look
>>>   at that in about a week's time (I'll be busy with other work the
>>>   next couple of days).
>>
>>This looks like a rather serious problem, so please take a look at
>>this.
>
>I've done more tests now, and the problem is that errors detected
>outside of sata_promise itself, typically timeouts, don't trigger
>the pdc_reset_port() call needed to bring the ATA engine behind the
>port back to sanity.

I did a round of regression tests which identified another
related but different problem.

In kernels 2.6.24 and 2.6.25 sata_promise would actually recover
from the timeouts, while in kernels 2.6.26 and 2.6.27 it would not.
Before 2.6.26 sata_promise explicitly used sata_std_hardreset, but
in the "make reset related methods proper port operations" commit
(a1efdaba2dbd6fb89e23a87b66d3f4dd92c9f5af), Tejun changed sata_promise
to use the hardreset it now inherits from ata_sff_port_ops, namely
sata_sff_hardreset. This change looks accidental. The main difference
between these two procedures is that the sff version will poll the
legacy status register until the port becomes ready.

Changing sata_promise to use sata_std_hardreset in 2.6.26/.27
makes the EH after the timeouts much more reliable. Not as
tidy as with the previous ->prereset fix, but still working.

/Mikael
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