Re: [RFC] Adding MTD to device tree

Segher Boessenkool
2006-08-12T13:46:49Z

>> Required properties:
>> - device_type : one of "nand-flash", "nor-flash", or "rom".
>
> There are more than just those kinds of MTDs. There's dataflash,
> AG-AND, NVRAM, ioremappable DRAM, etc. I'd prefer it to just be
> called
> "flash". See more below.

Existing firmwares call it "rom", "nvram", "flash". All of those
are easy; and I have really no opinion how all the weirdo nand-flash
etc. interfaces should be handled.

device_type communicates to the device-tree consumer what other
properties to expect in this node -- it does not indicate the exact
programming model of the device itself.

I suspect for most nand-flash you can get away with a device_type
of "nand-flash"; for some you might have to specify something more
detailed.

>> - model : an identifier for the actual controller chip used.
>
> Meaning what exactly? Lots of NOR flash doesn't have a "controller".

Lots of those chips from different vendors are pin-compatible as well,
so you cannot really hardcode one specific model number. I don't see
this information being very useful anyway. Instead, in most cases, the
information you're really after is the programming interface for the
device. And that goes...

>> - compatible : Should be the name of the MTD driver. For
>> type "rom", this is most likely "physmap".
>
> This I agree with, but Sergei already had this. And since you're
> specifying the name of the MTD driver, that typically already knows
> what
> type of chip it's talking to.

"compatible" contains a list, most specific first. So for example
for a NOR-flash it could be "jedec-flash,nor-flash,flash" or whatnot.
(Btw: no comma's, but 0-chars in the actual properties!)

Segher