linux-kernel - Re: [PATCH v2 1/2] EDAC/amd64: Check register values from all UMCs

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Date:   Thu, 30 Dec 2021 12:36:44 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Yazen Ghannam <yazen.ghannam@....com>
Cc:     linux-edac@...r.kernel.org, linux-kernel@...r.kernel.org,
        mchehab@...nel.org, tony.luck@...el.com, james.morse@....com,
        rric@...nel.org, Smita.KoralahalliChannabasappa@....com,
        william.roche@...cle.com
Subject: Re: [PATCH v2 1/2] EDAC/amd64: Check register values from all UMCs

On Thu, Dec 16, 2021 at 04:08:18PM +0000, Yazen Ghannam wrote:
> No, that's a good question. And actually the assumption is incorrect. It is
> allowed to have different DIMM types in a system though all DIMMs on a single
> UMC must match.

Oh fun, really?!

So a single system can have DDR4 *and* DDR5 on the same board?!

So then that

	pvt->dram_type

is insufficient to store the DIMM type for a pvt. If you have multiple
UMCs on a pvt and all have different type DIMMs, then you need the
relevant DIMM type when you dump it in sysfs...

Which then means, you need ->dram_type to be per UMC...

And also, I'm assuming the hw already enforces that DIMMs on a single
UMC must match - it simply won't boot if they don't so you don't have to
enforce that, at least.

> Do you recommend a follow up patch or should this one be reworked?

This one is insufficient, I'm afraid.

One way to address this is, you could use pvt->umc at the places where
dram_type is used and assign directly to the dimm->mtype thing. But then
you'd need a way to map each struct dimm_info *dimm to the UMC so that
you can determine the correct DIMM type.

Which would make pvt->dram_type redundant and can be removed.

Or you might have a better idea...

HTH.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette