Common Flash Interface v1.4 and MTD support in Linux-2.4.4 kernel

[Josh Boyer]

On Tue, 2006-02-07 at 16:33 +1300, David Antliff wrote:
> 
> 
> I am working on an MPC852 embedded platform based on the Denx
> Linux-2.4.4 port.

To note, 2.4.4 is ancient.  And this whole question would be better
asked on the MTD mailing list.

> 
> We have an existing device with a fixed-flash (AMD-type) conforming to
> CFI (Common Flash Interface) version 1.2. Linux-2.4.4 supports this
> device when used by the Memory Tech Device Driver (MTD). This device has
> a single region ('plane'?) or at least constant geometry across the
> device. MTD in 2.4.4 has no problems dividing this up into a bunch of
> block devices (partitions for read-only filesystems).

Yep.

> 
> A newer version has a different flash chip - an Intel P30 flash with
> multiple regions - it has two types of geometries as it is configured
> for 'boot' operation. It also conforms to CFI version 1.4. Unfortunately
> the Linux-2.4.4 MTD driver rejects this as unsupported based on CFI
> version and hard-coding it in "kinda" works - the partition devices are
> readable but the driver complains bitterly about non-alignment with
> erase blocks. I suspect the driver is picking up parameters from the
> first region (which covers the first set of blocks) and trying to use
> this across the device. One thing I don't understand yet - as the first
> region uses block sizes that are an integer division of those in the
> second region I'm not sure why the boundaries don't align when I am
> using the 2nd-region block size to define the partition boundaries.

P30 support was just recently added to the 2.6 kernel.

> 
> 
> What I am looking for is some advice please - what do you think is the
> best course of action in this situation? 
> 
> There will be others but so far I am considering:
> 
> 1. back-port the CFI code from a newer 2.4 kernel to support CFI v1.4.
>  - does anybody know the state of MTD in later versions? What would be a
> good version to source from?

There is no support for CFI 1.4 in any 2.4 kernel.  You'd have to
backport from 2.6

> 
> 2. integrate code found here and try and understand how it works:
> http://lists.infradead.org/pipermail/linux-mtd/2001-November/003645.html

That won't solve all of your problems.

> 
> 
> What would you suggest? Yes, I am happy for a 'quick fix' but if there
> isn't one or it's too risky I am willing to invest the time in doing it
> right.

'quick fix' is to pull the changes from cfi_cmdset_0001.c in MTD CVS
back into your kernel.  But I'm not sure how quick that will be given
that your kernel is very very old.

josh