Subject: Re: [PATCH] Configure IDE probe delays
From: Alan Cox <alan@lxorguk.ukuu.org.uk>
To: Mark Lord <lkml@rtr.ca>
Cc: bzolnier@milosz.na.pl, Lee Revell <rlrevell@joe-job.com>,
       Greg Stark <gsstark@mit.edu>,
       Denis Vlasenko <vda@port.imtp.ilyichevsk.odessa.ua>,
       Todd Poynor <tpoynor@mvista.com>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       tim.bird@am.sony.com, dsingleton@mvista.com
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On Mer, 2004-09-01 at 14:20, Mark Lord wrote:
> LBA48 is only needed when (1) the sector count is greater than 256,
> and/or (2) the ending sector number >= (1<<28).

I've played with this a bit and in the -ac IDE code it can drop back
to LBA28 for devices that are small enough not to need LBA48 when the
controller only supports PIO for LBA48 modes (eg some ALi) as 2.4-ac
did. 

> I regularly include this optimisation in the drivers I have been
> working on since LBA48 first appeared.

It isn't always a win. You get cut down to 256 sectors per I/O which for
some workloads has a cost and you need to factor that into the command
issue choice as well as the last sector number being accessed.

Alan

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