Date:	Sun, 17 May 2009 11:59:56 -0600
From:	Robert Hancock <hancockrwd@...il.com>
To:	Martin Lottermoser <Martin.Lottermoser@...nline.de>
CC:	linux-kernel@...r.kernel.org
Subject: Re: PATA DMA problem leading to kernel panic on reading movie DVDs

Martin Lottermoser wrote:
> Hello,
> 
> newer versions of the Linux kernel overestimate my DVD drive's
> DMA capabilities, leading either to DMA being disabled or a kernel
> panic.
> 
> My setup is:
> 
>   Motherboard: ASUS P4C800-E Deluxe
>     South bridge: ICH5R
>       IDE Interface Controller (PATA): Intel 82801EB/ER (PCI: 8086:24db)
>   DVD drive: Samsung SH-S202N, attached as hdc.
>     There is also an older CD writer (Lite-On LTR-52327S) attached as
>     hdd.
>   Operating system: Debian 5.0.0 with security updates
> 
> On upgrading from Debian 4.0 (Linux 2.6.18) to 5.0 (Linux 2.6.26) I
> found that trying to play movie DVDs with vlc (VideoLAN media player)
> led to DMA being disabled:
> 
>   hdc: cdrom_decode_status: status=0x51 { DriveReady SeekComplete Error }
>   hdc: cdrom_decode_status: error=0x40 { LastFailedSense=0x04 }
>   ide: failed opcode was: unknown
>   <4 more identical groups of these messages>
>   hdc: DMA disabled
>   hdc: ide_intr: huh? expected NULL handler on exit
>   hdc: ATAPI reset complete

Looks like kind of a comedy of errors. It failed to indicate what the 
failed command was (though, it seems like the failed opcode is always 
unknown with the IDE drivers), disabled DMA incorrectly, then seemingly 
confused itself.

Seems like the IDE layer grew some regressions at some point. You could 
try a newer (2.6.29) kernel. However, from a user perspective, quite 
likely you'll be happier ditching the IDE drivers and using libata 
instead, it tends to be better tested these days..

> 
> The resulting configuration is too slow to play movies. I booted the
> older kernel and everything was fine.
> 
> I then tested various versions of the Linux kernel where I happened to
> have the original sources. The most interesting results were:
> 
>   2.6.22.9      works, no errors visible in syslog
>   2.6.23.14     works, but syslog shows an error (see below)
>   2.6.24.3	DMA disabled
>   2.6.29.3	Kernel panic: Fatal exception in interrupt (ide_intr)
>                 on trying to open the DVD with vlc
> 
> The error message with 2.6.23.14 was:
> 
>   hdc: drive_cmd: status=0x51 { DriveReady SeekComplete Error }
>   hdc: drive_cmd: error=0x04 { AbortedCommand }
>   ide: failed opcode was: 0xec
> 
> This kernel as well as 2.6.22.9 also showed the following on booting:
> 
>   hdc: host side 80-wire cable detection failed, limiting max speed to UDMA33
> 
> This is correct: the drive is only capable of Ultra DMA mode 2 33.3 MB/s
> (see manufacturer's documentation) and is attached with a standard 40-wire
> ATA cable (black connectors for master and slave).
> 
> This led me to inspect other boot messages. With 2.6.18.3 I found:
> 
>   hdc: ATAPI 48X DVD-ROM DVD-R-RAM CD-R/RW drive, 2048kB Cache, UDMA(33)
> 
> 2.6.24.3 showed:
> 
>   hdc: UDMA/66 mode selected
>   ...
>   hdc: ATAPI 48X DVD-ROM DVD-R-RAM CD-R/RW drive, 2048kB Cache
> 
> In contrast, the hdd drive shows up with "UDMA/33 mode selected" up to
> and including 2.6.29.3.
> 
> I now use "hdparm -d1 -X udma2 /dev/hdc" with the Debian kernel 2.6.26
> and the drive works as desired. However, when querying the drive's
> capabilities with "hdparm -I", although the command terminates
> successfully and without any error messages (it shows
> 
>   DMA: mdma0 mdma1 mdma2 udma0 udma1 *udma2 udma3 udma4
> 
> ), on inspecting the syslog I find, on each invocation, a similar
> error message as above with 2.6.23.14:
> 
>   hdc: task_in_intr: status=0x51 { DriveReady SeekComplete Error }
>   hdc: task_in_intr: error=0x04 { AbortedCommand }
>   ide: failed opcode was: 0xec
> 
> Interestingly enough, this happens also when calling "hdparm -I" on hdd.
> There are also error messages
> 
>   hdc: set_drive_speed_status: status=0x51 { DriveReady SeekComplete Error }
>   hdc: set_drive_speed_status: error=0x04 { AbortedCommand }
>   ide: failed opcode was: unknown
> 
> from the boot phase.
> 
> Therefore there is still something wrong. Any suggestions on what that
> is and how to fix it? (Answers preferably through "Cc:", but I'll also
> try and follow the thread through list archives.)
> 
> Martin Lottermoser
> --
> Martin Lottermoser             Martin.Lottermoser at _REMOVE_t-online.de
> Greifswaldstrasse 28
> 38124 Braunschweig             http://home.vrweb.de/martin.lottermoser
> Germany

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