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: <48FD9A90.8000205@gmail.com>
Date:	Tue, 21 Oct 2008 18:02:08 +0900
From:	Tejun Heo <htejun@...il.com>
To:	Mikael Pettersson <mikpe@...uu.se>
CC:	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)

Hello,

Mikael Pettersson wrote:
> Tejun Heo writes:
>  > Hello, Mikael.
>  > I would put this into ->hardreset itself as the controller can also
>  > get out of sync with reality during reset.
> 
> The only thing I see going on between prereset and (hard/soft)reset
> is an optional freeze, so I don't see why moving the pdc_reset_port()
> into the beginning of hardreset() would make any difference.
> 
> sata_promise currently uses the ->hardreset and ->softreset inherited
> from ata_sff_port_ops, so it would need to override both to ensure that
> we always do pdc_reset_port() before libata does its thing. That's why
> I felt doing that in ->prereset would be the right solution.

Hmm.. reset sequence goes on like the following.

 1. prereset
 2. hardreset, if fail, retry
 3. follow-up softreset if requested, if fail, goto #2
 4. postreset, if successful

So, if some PHY event happens while the reset is waiting for device
readiness and makes the controller state go out of sync with the
drive.  ->prereset() will NOT be called for the following retry.

As a rule, ->hardreset should be able to reset the controller from all
possible situations.  ->prereset can be used to smooth out initial
reset tries (ie. during initial probing, waiting for device readiness
before SRST for SFF controllers w/o hardreset) but at best its
function is advisory.  When things go wrong, ->hardreset should be
able to provide solution whatever state the controller is in.

If both hard and soft resets work better with the controller reset
added, I think it would be best to override both.

Thanks.

-- 
tejun
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