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

On Tue, Sep 7, 2021, at 22:48, Alyssa Rosenzweig wrote:

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+      - 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.

That raises another issue ... how do we know the M3 code works at all
without TB support yet? It "looks" correct but some of the IRQ handling
stuff is nontrivial.

Enabling the mailbox interface just requires a few clocks to be ungated.
Then I injected messages manually to verify that the code works.
In addition I also brought up parts of the Thunderbolt controller which
then allowed the co-processor on the other end of the mailbox to boot.
After that I was also able to successfully talk to that processor using
the same protocol used by most other processors.

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+  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.

D'oh, right, retracted. (Both this comment and the corresponding comment
on the driver itself). Sorry about that.

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+  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.

Good enough for me, thanks for clarifying 👍

Commit r-b, though Rob will surely point out problems and I'll need to
rereview 😉

Thanks!



Sven