Subject: Re: OF compatible MTD platform RAM driver ?

From: Sergei Shtylyov <[email-masked]>
Date: Tue, 25 Mar 2008 19:23:23 +0300

Laurent Pinchart wrote:

>>>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.

    Well, I might have gone too far here -- it should be a real device 
(spec'ed in Device Support Extensions recommended practice). It's just that 
the spec didn't mention "reg" property, only "#bytes" (the device capacity). 
So, it may be worth considering...

>>>                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.

    Heh, there was a whole company against mentioning "mtd" when we started 
working on this (of course, the first idea was to call the flash device type 
"mtd"). I don't think "mtd" looks good here -- I'd suggest "flash-ram" (if 
this is just a linearly mapped NVRAM).

> Best regards,

WBR, Sergei