linux-kernel - Re: [PATCH 3/3] e820: Add the unknown-12 Memory type (DDR3-NvDIMM)

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Message-ID: <CAPcyv4i5WfR48hmGwqLDgTFRpUPaAxusHXKKUKY4FBxu1Mqm+w@mail.gmail.com>
Date:	Thu, 5 Mar 2015 12:56:01 -0800
From:	Dan Williams <dan.j.williams@...el.com>
To:	Boaz Harrosh <boaz@...xistor.com>
Cc:	Ingo Molnar <mingo@...hat.com>, X86 ML <x86@...nel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	"Roger C. Pao" <rcpao.enmotus@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-nvdimm <linux-nvdimm@...ts.01.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Matthew Wilcox <willy@...ux.intel.com>,
	Andy Lutomirski <luto@...capital.net>,
	Christoph Hellwig <hch@...radead.org>,
	Ross Zwisler <ross.zwisler@...ux.intel.com>
Subject: Re: [PATCH 3/3] e820: Add the unknown-12 Memory type (DDR3-NvDIMM)

On Thu, Mar 5, 2015 at 2:24 AM, Boaz Harrosh <boaz@...xistor.com> wrote:
>
> There are multiple vendors of DDR3 NvDIMMs out in the market today.
> At various stages of development/production. It is estimated that
> there are already more the 100ds of thousands chips sold to
> testers and sites.
>
> All the BIOS vendors I know of, tagged these chips at e820 table
> as type-12 memory.
>
> Now the ACPI comity, as far as I know, did not yet define a
> standard type for NvDIMM. Also, as far as I know any NvDIMM
> standard will only be defined for DDR4. So DDR3 NvDIMM is
> probably stuck with this none STD type.

There's no relation between E820 types and DDR technology revisions.

> I Wish and call the ACPI comity to Define that NvDIMM is type-12.
> Also for DDR4
>
> The motivation of this patch is to be able to differentiate
> this NvDIMM type from a real future "unknown-reserved" type.
>
> In this patch I name type-12 "unknown-12". This is because of
> ACPI politics that refuse to reserve type-12 as DDR3-NvDIMM

It's not "politics".  Setting standards takes time and the platforms
in question simply jumped the gun to enable a proof-of-concept.

> and members keep saying:
>         "What if ACPI assigns type-12 for something else in future"
>
> [And I say: Then just don't. Please?]

Once a standard number is assigned, platform firmwares can update
type-12 to that number.  We might consider a compile time override for
these niche/pre-standard systems that can't/won't update, but it's not
clear to me that we even need to go that far.
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