linux-kernel - Re: [PATCH 2/3] dt-bindings: mailbox: Add Apple mailbox bindings

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Message-Id: <ff66c30d-1b43-43d3-a4b0-02fe7d346118@www.fastmail.com>
Date:   Tue, 07 Sep 2021 22:26:17 +0200
From:   "Sven Peter" <sven@...npeter.dev>
To:     "Alyssa Rosenzweig" <alyssa@...enzweig.io>
Cc:     "Jassi Brar" <jassisinghbrar@...il.com>,
        "Rob Herring" <robh+dt@...nel.org>,
        "Mark Kettenis" <mark.kettenis@...all.nl>,
        "Hector Martin" <marcan@...can.st>,
        "Mohamed Mediouni" <mohamed.mediouni@...amail.com>,
        "Stan Skowronek" <stan@...ellium.com>, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] dt-bindings: mailbox: Add Apple mailbox bindings

Hi,


On Tue, Sep 7, 2021, at 20:56, Alyssa Rosenzweig wrote:
> > +      - description:
> > +          M3 mailboxes are an older variant with a slightly different MMIO
> > +          interface still found on the M1.
> > +        items:
> > +          - const: apple,t8103-m3-mailbox
> 
> Would be nice to document an example of where an M3 mailbox is found.

Sure, I can add a comment that this is used for the coprocessor controlling Thunderbolt.

> 
> > +  interrupts:
> > +    minItems: 4
> > +    items:
> > +      - description: send fifo is empty interrupt
> > +      - description: send fifo is not empty interrupt
> > +      - description: receive fifo is empty interrupt
> > +      - description: receive fifo is not empty interrupt
> > +
> > +  interrupt-names:
> > +    minItems: 4
> > +    items:
> > +      - const: send-empty
> > +      - const: send-not-empty
> > +      - const: recv-empty
> > +      - const: recv-not-empty
> 
> If the names became not-constant the asprintf thing goes away, not sure
> that's better or worse.

I'm not sure I understand your comment here. This property just gives a name
to the interrupts so that they can be referenced by that instead of a magic
number between 0 and 4 in the driver.

> 
> > +  clocks:
> > +    description:
> > +      Reference to the clock gate phandle(s) if required for this mailbox.
> > +      Optional since not all mailboxes are attached to a clock gate.
> 
> Do we do anything with the clocks at this point?
> 

The device tree bindings describe the hardware (as best as we can without proper
documentation) and some of these mailboxes have clock gates which need to be turned
on before accessing their MMIO. This driver already tries to do that and works fine
with the downstream clock driver(s) we have.



Sven