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 ?
[EMAIL PROTECTED],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...
The nvram device descrived in the Device Support Extensions is probably meant to describe the kind of nvram found in RTC chips.
Well, that is only an assumption -- actually, the sentense in the description of the "#bytes" prop about the typical size being from 4 to 32K speaks against it. The details of NVRAM implementation are hidden behind read/write/seek methods.
That memory isn't directly accessible.
That's what we have a "compatible" prop for. ;-)
As the spec doesn't mention this explicitely we could still reuse the nvram device type for direct-mapped battery-backed ram. I have no strong opinion for or against that.
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
[EMAIL PROTECTED],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).
I'm fine with "flash-ram" (even thought it looks a bit weird). I'll prepare a patch.
Yeah. I forgeot that "flash" means EEPROM. Actually, the main facts about the NVRAM that I'd want to be stated in the "compatible" property is that it's non-volatile and directly/lineraly mapped... Just "nvram" doesn't seem enopugh, maybe "linear-nvram" is. And we can specify "device_type" of "nvram" indeed (and #size).
Best regards,
WBR, Sergei _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@ozlabs.org https://ozlabs.org/mailman/listinfo/linuxppc-dev
