linux-kernel - Re: [PATCH 1/1] pata_it821x: fix lost interrupt with atapi devices

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Message-ID: <46EE5033.7060708@garzik.org>
Date:	Mon, 17 Sep 2007 06:00:19 -0400
From:	Jeff Garzik <jeff@...zik.org>
To:	Tejun Heo <htejun@...il.com>
CC:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Mikael Pettersson <mikpe@...uu.se>,
	Jeff Norden <jeff@...h.tntech.edu>, alan@...hat.com,
	linux-kernel@...r.kernel.org, Albert CC Lee <albertcc@...ibm.com>,
	IDE/ATA development list <linux-ide@...r.kernel.org>
Subject: Re: [PATCH 1/1] pata_it821x: fix lost interrupt with atapi devices

Tejun Heo wrote:
> [cc'ing Albert and linux-ide]
> 
> Alan Cox wrote:
>> /from the media. */
>>>  > +	if (qc->nbytes < 2048)
>>>  > +		return -EOPNOTSUPP;
>>>  > +
>>>  >  	/* No ATAPI DMA in smart mode */
>>>  >  	if (itdev->smart)
>>>  >  		return -EOPNOTSUPP;
>>>  > 
>>>
>>> This looks like a gross hack. Aren't you supposed to inspect
>>> the command instead and whitelist the ones you know are OK,
>>> like pata_pdc2027x.c and sata_promise.c do?
>> It does seem to be about transfer size in the IT821x case not commands.
>> It may be to do with how we issue ATAPI command transfer sizes from high
>> up (patch went to Jeff) but for now this is definitely the right approach
>>
>> Reviewed-by: Alan Cox <alan@...hat.com>
> 
> I wonder whether we should be using similar check in generic path too.
> We have quite a few cases where MWDMA ATAPI devices choking on commands
> with small transfer sizes.  I don't think we'll experience significant
> performance regression with this applied and even if there is some, it's
> far better to have slightly slower working device.
> 
> What do you guys think?

Need to look at, or know, a standard profile of submitted commands. 
It's quite possible some high performance commands want this, where 
possible.

	Jeff


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