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

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Message-ID: <CALCETrX6hLg+VPU-8voTFz+uChUdYf_JYg5iEwr6skEHp4R=Dg@mail.gmail.com>
Date:	Thu, 5 Mar 2015 15:09:45 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	Dan Williams <dan.j.williams@...el.com>
Cc:	Boaz Harrosh <boaz@...xistor.com>, 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>,
	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 12:56 PM, Dan Williams <dan.j.williams@...el.com> wrote:
> 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.

I will be shocked if a standard of this form ever appears.  Modern
systems *don't have e820*.  The BIOSes that are using this type 12
hack are awful throwbacks.

--Andy
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