linux-kernel - Re: [RFC PATCH 6/9] memory: apple: Add apple-mcc driver to manage MCC perf in Apple SoCs

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Date:   Thu, 14 Oct 2021 10:04:51 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>
To:     Hector Martin <marcan@...can.st>,
        linux-arm-kernel@...ts.infradead.org
Cc:     Alyssa Rosenzweig <alyssa@...enzweig.io>,
        Sven Peter <sven@...npeter.dev>, Marc Zyngier <maz@...nel.org>,
        Mark Kettenis <mark.kettenis@...all.nl>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Viresh Kumar <vireshk@...nel.org>, Nishanth Menon <nm@...com>,
        Catalin Marinas <catalin.marinas@....com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Kevin Hilman <khilman@...nel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        linux-clk@...r.kernel.org, devicetree@...r.kernel.org,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 6/9] memory: apple: Add apple-mcc driver to manage MCC
 perf in Apple SoCs

On 14/10/2021 09:52, Hector Martin wrote:
> On 14/10/2021 16.36, Krzysztof Kozlowski wrote:

(...)

> 
>>> Ah, I didn't realize that was a valid option for MODULE_LICENSE. I guess
>>> anything containing "GPL" works with EXPORT_SYMBOL_GPL?
>>
>> I don't think exporting symbols is related to how you license your code.
> 
> It is; only modules with a GPL-compatible MODULE_LICENSE get to use 
> symbols exported via EXPORT_SYMBOL_GPL.

Although there might be such correlation but it's not a rule. You can
have a GPL module exporting symbols without GPL requirement
(EXPORT_SYMBOLS). You can have a GPL+MIT module exporting symbols as
GPL. Obviously you cannot have a non-GPL module, as we do not accept
these and there is no such choice.

So answering your question that "GPL" works with EXPORT_SYMBOL_GPL -
everything is GPL but it works with both EXPORT_SYMBOL and
EXPORT_SYMBOL_GPL.

> 
> See kernel/module.c for the symbol lookup logic and 
> include/linux/license.h for the logic to check the string (seems like 
> "Dual MIT/GPL" is explicitly whitelisted there).

Not related to export symbol. It is used for determining the tainted
kernel via other licenses.

> 
> Of course, this is a futile effort, as ~every time I see a proprietary 
> module in some embedded device, it either falsely declares itself to be 
> GPL, or they have a shim module that re-exports GPL symbols as non-GPL.
> 

This is being removed soon (or already).


Best regards,
Krzysztof