linux-kernel - Re: ata_tf_read

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Date:	Sun, 16 Aug 2009 11:15:31 +0900
From:	Tejun Heo <htejun@...il.com>
To:	Atsushi Nemoto <anemo@....ocn.ne.jp>
CC:	Jeff Garzik <jgarzik@...ox.com>, linux-ide@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: ata_tf_read_block() question

Hello, Atsushi.

Atsushi Nemoto wrote:
> I have a question on CHS calculation in ata_tf_read_block().
> 
> The calculation in ata_tf_read_block() is:
> 	block = (cyl * dev->heads + head) * dev->sectors + sect;
> 
> but ata_build_rw_tf() does:
> 	track = (u32)block / dev->sectors;
> 	cyl   = track / dev->heads;
> 	head  = track % dev->heads;
> 	sect  = (u32)block % dev->sectors + 1;
> 
> It seems inconsistent.  The correct calculation is:
> 	block = (cyl * dev->heads + head) * dev->sectors + sect - 1;
> isn't it?

Yes, indeed.

> I don't have any real problem.  Just noticed by code reading.

ata_tf_read_block() currently is used only when reporting failed block
address to upper layer so off-by-one bug there wouldn't be too
visible, especially for the venerable CHS addressing.

Care to submit a patch w/ warning message and capping for sect == 0
case?

Thanks.

-- 
tejun
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