From: Sergei Shtylyov <sshtylyov@ru•mvista.com>
To: Laurent Pinchart <laurentp@cse-semaphore•com>
Cc: ben@simtec•co.uk, linuxppc-dev@ozlabs•org,
linux-mtd@lists•infradead.org,
David Gibson <david@gibson•dropbear.id.au>
Subject: Re: OF compatible MTD platform RAM driver ?
Date: Tue, 25 Mar 2008 20:02:08 +0300 [thread overview]
Message-ID: <47E93010.5090904@ru.mvista.com> (raw)
In-Reply-To: <200803251744.46001.laurentp@cse-semaphore.com>
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...
> 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
>>> 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).
> 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
next prev parent reply other threads:[~2008-03-25 17:00 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-03-10 15:06 OF compatible MTD platform RAM driver ? Laurent Pinchart
2008-03-10 17:00 ` Rune Torgersen
2008-03-11 0:45 ` David Gibson
2008-03-11 10:39 ` Laurent Pinchart
2008-03-11 22:40 ` David Gibson
2008-03-25 14:36 ` Laurent Pinchart
2008-03-25 15:29 ` Sergei Shtylyov
2008-03-25 15:51 ` Laurent Pinchart
2008-03-25 16:23 ` Sergei Shtylyov
2008-03-25 16:44 ` Laurent Pinchart
2008-03-25 17:02 ` Sergei Shtylyov [this message]
2008-03-25 17:23 ` Laurent Pinchart
2008-03-25 17:37 ` Sergei Shtylyov
2008-03-25 17:56 ` Rune Torgersen
2008-03-25 18:14 ` Laurent Pinchart
2008-03-26 12:53 ` Sergei Shtylyov
2008-03-27 9:13 ` Laurent Pinchart
2008-03-27 10:03 ` David Gibson
2008-03-27 12:23 ` Sergei Shtylyov
2008-03-28 0:07 ` David Gibson
2008-03-28 12:31 ` Sergei Shtylyov
2008-03-27 14:31 ` Laurent Pinchart
2008-03-28 0:09 ` David Gibson
2008-03-30 18:15 ` Segher Boessenkool
2008-03-30 21:16 ` Paul Mackerras
2008-03-30 22:39 ` Segher Boessenkool
2008-03-31 0:42 ` Paul Mackerras
2008-03-31 0:59 ` Segher Boessenkool
2008-03-31 1:24 ` Segher Boessenkool
2008-03-31 8:21 ` Laurent Pinchart
2008-03-31 12:21 ` Segher Boessenkool
2008-03-26 15:06 ` Segher Boessenkool
2008-03-26 15:40 ` Sergei Shtylyov
2008-03-27 9:24 ` Laurent Pinchart
2008-03-30 18:12 ` Segher Boessenkool
2008-03-26 15:09 ` Segher Boessenkool
2008-03-11 15:00 ` Rune Torgersen
2008-03-11 22:41 ` David Gibson
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=47E93010.5090904@ru.mvista.com \
--to=sshtylyov@ru$(echo .)mvista.com \
--cc=ben@simtec$(echo .)co.uk \
--cc=david@gibson$(echo .)dropbear.id.au \
--cc=laurentp@cse-semaphore$(echo .)com \
--cc=linux-mtd@lists$(echo .)infradead.org \
--cc=linuxppc-dev@ozlabs$(echo .)org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox