linux-kernel - Re: [bisected] 2.6.31 regression sis5513 PIO Mode 0 hang

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Message-Id: <20091004.205848.109978798.davem@davemloft.net>
Date:	Sun, 04 Oct 2009 20:58:48 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	david@...es.net
Cc:	hancockrwd@...il.com, linux-kernel@...r.kernel.org,
	d.stussy@...oo.com, joao.ramos@...v.pt, torvalds@...l.org,
	rjw@...k.pl, vojtech@...e.cz
Subject: Re: [bisected] 2.6.31 regression sis5513 PIO Mode 0 hang

From: David Fries <david@...es.net>
Date: Sun, 4 Oct 2009 21:55:50 -0500

> First, if I'm going to do much debugging, how would I force the
> ethernet device to come up first so I have netconsole?
> 
> How is the problem patch,
> +       ide_port_for_each_dev(i, drive, hwif) {
> +               if (port_ops && port_ops->set_pio_mode)
> +                       port_ops->set_pio_mode(drive, 0);
> +       }
> 
> Different from using hdparm to set the mode?  I do this,
> hdparm -p 0 /dev/hda
> hdparm -X pio0 /dev/hda
> and the benchmarks give me about what I would expect 7MB/s instead of
> the normal 40MB/s.
> 
> Then I can re-enable with,
> hdparm -p 4 /dev/hda
> hdparm -X udma5 /dev/hda
> hdparm -d 1 /dev/hda
> hda: UDMA/100 mode selected
> and the drive is back up to speed, and obviously the kernel didn't
> freeze.  Should there be anything different between what the patch
> tried, and and hdparm's doing, other than kernel initiated and start
> and a user program later on?

>From your original hang trace I can only guess that the problematic
sequence is putting your CDROM into PIO0, then putting it into
PIO4, and then immediately reading the TOC.

This is what the ide-cd.c code does right about where you get the
hang.

Debugging this further is really totally pointless for a subsystem
that should be in deep maintainence mode, so I'm just going to
revert.

Thanks.
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