OF compatible MTD platform RAM driver ?
Sergei Shtylyov
sshtylyov at ru.mvista.com
Tue Mar 25 12:23:23 EDT 2008
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 at 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 at 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
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