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

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Message-ID: <46EE09D3.9010201@gmail.com>
Date:	Mon, 17 Sep 2007 07:00:03 +0200
From:	Tejun Heo <htejun@...il.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
CC:	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

[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?

-- 
tejun

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