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From: David Zaffiro <davzaffiro@tasking.nl>
To: linux-kernel@vger.kernel.org
Cc: waltabbyh@comcast.net
Subject: Re: [PATCH] pdcraid and weird IDE geometry
Date: Thu, 17 Jul 2003 14:19:03 +0200	[thread overview]
Message-ID: <3F169437.8000802@_netscape_._net_> (raw)
In-Reply-To: <3F160965.7060403@comcast.net>

I don't think this has any to do with the calculation, you probably just have to use:

CONFIG_PDC202XX_FORCE=y

(well, combined with...

CONFIG_BLK_DEV_PDC202XX_NEW=y
CONFIG_BLK_DEV_PDC202XX=y
CONFIG_BLK_DEV_ATARAID=y
CONFIG_BLK_DEV_ATARAID_PDC=y

...and a lot of other options...)

With 2.4.20 the FORCE option had to be set at "n", now it should be set at "y".


> The calc_pdcblock_offset function calculates lba by taking the capacity
> of the drive and dividing it by (head * sector), multiplying the result
> times (head * sector) and subtracting the sector (SPT) count.
> Unfortunately, with the strange geometry reported by the new drive,
> using INTs to store these values will fail. 


Avoiding floating-point precision,  this would do the same as your calculation:

lba = ideinfo->capacity - ideinfo->sect;


However, I don't think the expression "fails". the way it is expressed now, it will divide something integer-wise and then multiply it with the same value (and then minus sect), thus I assume this was intended: To round the capacity value to the next multiple of (head * start),  and then do a minus sect...

I don't think any hardcore programmer ever does a integerwise divide /before/ an integerwise multiply without a very good reason... (And don't give me that "you'd be surprised"!!!)



  parent reply	other threads:[~2003-07-17 12:06 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2003-07-17  2:26 Walt H
2003-07-17  8:49 ` Arjan van de Ven
2003-07-17 14:37   ` Walt H
2003-07-17 14:58     ` Alan Cox
2003-07-17 15:34       ` Jeff Garzik
2003-07-17 16:03         ` Andries Brouwer
2003-07-17 15:34       ` Andries Brouwer
2003-07-18  2:33         ` Walt H
2003-07-18  8:58           ` Andries Brouwer
2003-07-18 13:56             ` Walt H
2003-07-17 12:19 ` David Zaffiro [this message]
2003-07-18 14:51 Walt H

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