Subject: READ SCSI cmd seems to fail on SATA optical devices...
From: Mathieu Fluhr <mfluhr@nero.com>
To: jgarzik@pobox.com
Cc: linux-ide@vger.kernel.org, linux-kernel@vger.kernel.org
Content-Type: text/plain
Organization: Nero AG
Date: Mon, 13 Nov 2006 17:19:36 +0100
Message-Id: <1163434776.2984.21.camel@de-c-l-110.nero-de.internal>
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Hello,

I recently tried to burn some datas on CDs and DVD using a SATA burner
and the latest 2.6.18.2 kernel... using NeroLINUX. (It is controlling
the device by sending SCSI commands over the 'sg' driver)

The burn process works like a charm, no problems at all. But it seems
that there are some slight problems with the READ scsi cmd:
Inside our software, we have a verification routine that will make a
sector-by-sector verification to check that everything that has been
written is OK.

The problem is that, on SATA devices controlled by libata, on some big
files (like for example a 600 MB file) the READ command seems to fail
and outputs garbage (not 1 or 2 bytes diff, but the whole buffer).
 -> This problem does not come out everytime, and each time on    
    different sectors.

Please note that:
- it is not chipset dependant (tested on nforce4 and sii3114)
- it is not medium or device dependant


I debugged a little bit and found out the following:

- Our software tries to guess the bus type for each device by using
INQUIRY SCSI cmds. For SATA devices, it always returns SCSI. 
(which according to the source code is normal -> libata-scsi.c:2396)

- When I force the bus type to be IDE, our software will then send ATA
commands. In this case, everything works like a charm. No errors at all.
 

I tried to debug a little bit more inside the source code of the Linux
kernel, but I must admit that I am really not so familiar with the
code... but it would be no problem to help anyone on this issue. :)

Best Regards,
Mathieu


-- 
*********************************************************
Mathieu Fluhr
Linux Software Engineer

Nero AG
Im Stoeckmaedle 18
76307 Karlsbad
Germany

E-mail: mfluhr@nero.com

NERO - BECAUSE TECHNOLOGY COUNTS
www.nero.com

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