Re: OF compatible MTD platform RAM driver ?

[Laurent Pinchart <laurentp@cse-semaphore.com>]

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On Tuesday 11 March 2008 23:40, David Gibson wrote:
> On Tue, Mar 11, 2008 at 11:39:08AM +0100, Laurent Pinchart wrote:
> > On Tuesday 11 March 2008 01:45, David Gibson wrote:
> > > On Mon, Mar 10, 2008 at 12:00:22PM -0500, Rune Torgersen wrote:
> > > > linuxppc-dev-bounces+runet=innovsys.com@ozlabs.org wrote:
> [snip]
> > > > We ran ito the same issue.
> > > > We did option 3, as it was efinetly the easiest,
> > >
> > > I think this is the best option in principle.
> > 
> > I'll implement that and post a patch after completing the ppc-to-powerpc 
> > migration.
> > 
> > > > here is the sram entry in our dts:
> > >
> > > Except that your implementation of it is not good.
> > >
> > > You're relying on the old obsolete flash binding with the "probe-type"
> > > field.  The solution should be adapted to the new approach which uses
> > > values in the "compatible" field to indicate various sorts of flash
> > > device.
> > 
> > What "compatible" values should I use for ROM and RAM mappings ?
> 
> That I'm not so sure of.  We'll need to find some consensus.
> 
> There may be existing IEEE1275 bindings for roms, which we should
> investigate.

Do you (or someone else here) have access to the IEEE1275 specification ? Is 
there any ROM binding in there ?

> Arguably RAM should be represented by a memory node, but 
> that's going to get messy for this sort of application.

We're talking about a very specific type of RAM, used for permanent storage 
with a battery backup. The RAM is really meant to be used as an MTD device 
and as such I think it makes sense to describe it as an mtd-compatible device 
on the local bus.

What about the following definition for the RAM node ?

        nvram@2,0000 {
                compatible = "mtd,ram";
                reg = <2 0x0000 0x00100000>;
                bank-width = <2>;
        };

Or should the node have a device-type property of either 'ram' or 'rom' with 
the compatible property just referencing MTD ?

Best regards,

-- 
Laurent Pinchart
CSE Semaphore Belgium

Chaussée de Bruxelles, 732A
B-1410 Waterloo
Belgium

T +32 (2) 387 42 59
F +32 (2) 387 42 75

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