Re: OF compatible MTD platform RAM driver ?

Laurent Pinchart
2008-03-25T15:51:46Z

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Hi Sergei,

On Tuesday 25 March 2008 16:29, Sergei Shtylyov wrote:
> Hello.
>
> Laurent Pinchart wrote:
>
> >>>>>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
>
> Yeah, and I can point you to it -- see the documantation section on
> http://www.openbios.org/...

Thanks a lot for the pointer.

> > there any ROM binding in there ?
>
> No. We initially called the flash devices that physmap_of driver
> controlled "rom" (I mean the "device_type" property) -- now this is obsoleted.
>
> >>Arguably RAM should be represented by a memory node, but
> >>that's going to get messy for this sort of application.
>
> Note that the OF "memory" type nodes do *not* represent RAM devices.
>
> > 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 {
>
> Note that there's a OF "device_type" of "nvram", so your (generic) device
> name seems to add some mess. (IIRC, that OF device type didn't actually
> represent a "real" device, and only served to provide access to NVRAM for OF).

Ok.

> > compatible = "mtd,ram";
>
> The part before comma should be a company name or a stock ticker. What did
> you mean here?

I didn't know that. Let's say I meant "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 ?
>
> The "device_type" properties are not required and their further creation
> has been discouraged on liunxppc-dev.

What about

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

ROMs could use "mtd-rom" for their compatible property.

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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