Re: [PATCH] powerpc: Create "rom" (MTD) device prpmc2800

[David Woodhouse <dwmw2@infradead.org>]

On Mon, 2007-06-04 at 07:04 +1000, Benjamin Herrenschmidt wrote:
> So you are saying that because the current linux MTD stuff can only
> probe (which doesn't always work), we should not put the proper chip
> interface type in the device-tree ?
> 
> Your argument makes no sense to me.
> 
> Put the proper interface informations in the device-tree, maybe some OS
> smarter than linux will make good use on it and maybe linux will be
> fixed at one point too (not by you, of course, you gave us that line
> often enough about not being paid to do the right thing).

In general, Linux is doing the right thing by probing.

There are two major command sets for NOR flash -- the Intel/Sharp
command set, and the AMD/Fujitsu command set.

There are also two major ways to detect flash chips -- the JEDEC probe
with magic numbers for mfr/chip ident, and the CFI ('Common Flash
Interface') probe which gets you tables of information about the chip,
including what optional command set extensions it has, etc.

You _can_ bypass the probe and pass straight through to the 'back-end'
chip driver. But unless you provide the CFI information you won't get to
use any of the optional chip features (or blacklist some of the
known-broken features). It doesn't make a lot of sense to try using the
back-end chip drivers directly. Just go through the normal probe
process, really.

If you really want to bypass the probe, then I suspect you want the full
CFI tables to be present in your OF properties.

-- 
dwmw2