linux-kernel - Re: libata/PATA: GPCMD_SET_STREAMING via SG

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Date:	Wed, 14 Nov 2007 11:41:37 -0500
From:	Mark Lord <lkml@....ca>
To:	Mark Lord <liml@....ca>
Cc:	Sebastian Kemper <sebastian_ml@....net>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: libata/PATA: GPCMD_SET_STREAMING via SG_IO does nothing

Mark Lord wrote:
> Sebastian Kemper wrote:
>> Hi Alan!
>>
>> On Tue, Nov 13, 2007 at 09:22:30PM +0000, Alan Cox wrote:
>>> It isn't a known issue, and it suprises me as SG_IO basically passes
>>> commands through to the drive. We don't support speed change via 
>>> xfermode
>>> setting but GPCMD_SET_STREAMING sohuld behave.
>>>
>>> Do you have a simple code example that shows the problem ?
>>
>> http://svn.mplayerhq.hu/mplayer/trunk/stream/stream_dvd.c?view=markup
> ..
> 
> That code is riddled with bugs, by the way.
> It fails to close/clean-up on just about every exit path.
> But apart from that, it does appear to issue the command.
> 
> Another way to the same thing is with "hdparm -E",
> which contrary to my earlier posting actually does
> seem to work already with libata.
> 
>> See dvd_set_speed(). The drive I'm using is an Optiarc DVD RW AD-7170A.
>> With the "old" ATA driver dvd_set_speed() works, with libata it doesn't.
> ..
> 
> Can you define "doesn't work" for me?
> How can I test this to see if it works one way or another ?
> 
> The command issue (ioctl) is not returning -1.
..

Ahh.. got it.  The host_status returned (not checked by that code) was 7,
which means "host error".

In this case, that's because the cmd_len is (16), which is too large for ATAPI.
It needs to be changed to (12) instead.

So this line:  sghdr.cmd_len = 12;
The code (apart from totally mishandling any kinds of errors) works after that.

-ml
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