linux-kernel - Re: [PATCH v2 2/7] dt-bindings: interrupt-controller: apple,aic2: New binding for AICv2

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Message-ID: <67171c2a-7601-6dfb-92b3-24c1ca971995@marcan.st>
Date:   Sat, 26 Feb 2022 06:58:34 +0900
From:   Hector Martin <marcan@...can.st>
To:     Rob Herring <robh@...nel.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Marc Zyngier <maz@...nel.org>, Sven Peter <sven@...npeter.dev>,
        Alyssa Rosenzweig <alyssa@...enzweig.io>,
        Mark Kettenis <mark.kettenis@...all.nl>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org
Subject: Re: [PATCH v2 2/7] dt-bindings: interrupt-controller: apple,aic2: New
 binding for AICv2

On 26/02/2022 05.19, Rob Herring wrote:
>> +properties:
>> +  compatible:
>> +    items:
>> +      - const: apple,t6000-aic
>> +      - const: apple,aic2
> 
> I feel I was sold on Apple doesn't change h/w and we're the 2nd chip in 
> and the h/w changed. Just my musings, but aic3 will be rejected. :(

Well yes, after not changing hardware for N phone/tablet generations,
they figured out they *finally* had to make some changes for real
desktop chips... (t8103 was a tablet chip they shoehorned into laptops;
t6000 is the first real laptop/desktop chip). This isn't the 2nd chip
in, this is the 26th chip in or so, and yet it's called AIC2 (by Apple
even)... We aren't starting from chip #1, just the first chip they
decided to *let* us put Linux on.

It's pretty clear that the t6000 changes were made with future-proofing
in mind. I guess we'll find out in a couple weeks, since the rumor mill
says M2 is coming. If I'm right and we end up needing *zero* kernel
changes to boot on M2, will you be happy? ;-)

>> +  apple,event-reg:
>> +    $ref: /schemas/types.yaml#/definitions/uint32
>> +    description:
>> +      Specifies the offset of the event register, which lies after all the
>> +      implemented die register sets, page aligned. This is not computable from
>> +      capability register values, so we have to specify it explicitly.
> 
> If this is last, then couldn't it be a 2nd 'reg' entry?
> 
> 'page aligned' is ambiguous. I assume that means 16K since that's what 
> Apple uses, but I might assume 4K not knowing that.

16K, and yeah, it could be a 2nd reg entry if you think that works
better. Makes sense.

-- 
Hector Martin (marcan@...can.st)
Public Key: https://mrcn.st/pub