linux-kernel - Qualcomm Kryo core compatibles

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Date:   Wed, 8 Mar 2023 11:44:38 +0100
From:   Konrad Dybcio <konrad.dybcio@...aro.org>
To:     lkml <linux-kernel@...r.kernel.org>,
        dt <devicetree@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>
Subject: Qualcomm Kryo core compatibles

Hi!

I was recently debating what to do about Qualcomm Kryo compatibles.

There are basically 3 cases:

1. Falkor/"real Kryo" - the (never shipped?) server platform & MSM8996

This one's easy, it's actually Kryo so it should stay Kryo.

2. Fake Kryo ("customized" Arm Cortex cores) (MSM8998-SM8x50)

This one's tough.. Qualcomm marketing material seems to sometimes say
Cortex, sometimes Kryo, sometimes "customized Cortex".. They do use
their own arm IMPLEMENTER_ID in the MIDR_EL1 register and their
PART_NUM values are not Arm-stock, but these cores don't seem to be
any special.. Maybe some irq lines are routed differently? Not sure.

My proposition here is to do:

"qcom,kryoXXX", "arm,cortex-ABC"

or

"qcom,kryoXXX-PQR", "arm,cortex-ABC"

where PQR is one of:
- silver (LITTLE cores)
- gold (big cores)
- gold_plus (prime core(s))

3. Arm cores modified within Arm implementation-defined allowance (SC8280XP+)

These cores report Arm IMPLEMENTER_IDs and actual Arm PART_NUMs, which would
suggest they're bone stock Arm Cortex cores, with some Qualcomm-iness coming
as part of implementation details which are.. expected since Cortex allows for
some IMPLEMENTATION DEFINED things. The only non-obvious part here is that
the REVISION field they report does not always seem covered by the Arm TRMs.

In this case I think going with

"arm,cortex-ABC"

is fine.. I already did this for 8550 and 8280xp and Rob seems to have liked it.

So, I suppose the real question is what to do about 2., should they stay as
they are, or maybe my proposition seems attractive?

Konrad