linux-kernel - Re: [PATCH 00/10] AXFS: Advanced XIP filesystem

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Date:	Mon, 15 Sep 2008 12:43:00 -0700
From:	"Jared Hulbert" <jaredeh@...il.com>
To:	"Jamie Lokier" <jamie@...reable.org>
Cc:	"Greg Ungerer" <gerg@...pgear.com>, Linux-kernel@...r.kernel.org,
	linux-embedded@...r.kernel.org,
	linux-mtd <linux-mtd@...ts.infradead.org>,
	"Jörn Engel" <joern@...fs.org>,
	tim.bird@...sony.com, cotte@...ibm.com, nickpiggin@...oo.com.au
Subject: Re: [PATCH 00/10] AXFS: Advanced XIP filesystem

>> >> I'm using Spansion MirrorBit S29GL128N, which reads at about 0.6 MByte/s.
>>
>> If you are using a GL, you'll probably find our P33 a good fit and at
>> competitive prices to GL as I understand it.  That's I think 50Mhz.
>
> What's a GL?  Never heard of it - all I can think of is OpenGL :-)

S29_GL_128N

> I'm not sure if cache is an option with this device - but would it
> make a difference anyway?

Well the first read takes 100ns (plus the other chipset overhead
300ns) but other reads in a page are only an extra 25ns each.  So your
benefit is not from having the entire executable in cache it's from
having the next 7 instructions in the cacheline for only an extra 25ns
each instead of 400ns.

> Interesting, thanks.  I'm not sure it's possible to change the way NOR
> is being used with this chip, and it'll be a while before it's
> economical to replace the board with a new design.

Usually these things can be fixed in the bootloader or by hacking the
kernel to tweak the relevant chipset registers.
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