linux-kernel - RE: [PATCH] dt-bindings: mailbox: xlnx,zynqmp-ipi-mailbox: Document msg region requirement

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Message-ID:
 <LV5PR12MB980465BAF86F179E5638016A92B5A@LV5PR12MB9804.namprd12.prod.outlook.com>
Date: Tue, 23 Dec 2025 10:48:50 +0000
From: "T, Harini" <Harini.T@....com>
To: Krzysztof Kozlowski <krzk@...nel.org>
CC: "jassisinghbrar@...il.com" <jassisinghbrar@...il.com>, "robh@...nel.org"
	<robh@...nel.org>, "krzk+dt@...nel.org" <krzk+dt@...nel.org>,
	"conor+dt@...nel.org" <conor+dt@...nel.org>, "Simek, Michal"
	<michal.simek@....com>, "Datta, Shubhrajyoti" <shubhrajyoti.datta@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org"
	<linux-arm-kernel@...ts.infradead.org>, "git (AMD-Xilinx)" <git@....com>
Subject: RE: [PATCH] dt-bindings: mailbox: xlnx,zynqmp-ipi-mailbox: Document
 msg region requirement

[Public]

Hi,

> -----Original Message-----
> From: Krzysztof Kozlowski <krzk@...nel.org>
> Sent: Monday, December 22, 2025 2:39 PM
> To: T, Harini <Harini.T@....com>
> Cc: jassisinghbrar@...il.com; robh@...nel.org; krzk+dt@...nel.org;
> conor+dt@...nel.org; Simek, Michal <michal.simek@....com>; Datta,
> Shubhrajyoti <shubhrajyoti.datta@....com>; linux-kernel@...r.kernel.org;
> devicetree@...r.kernel.org; linux-arm-kernel@...ts.infradead.org; git (AMD-
> Xilinx) <git@....com>
> Subject: Re: [PATCH] dt-bindings: mailbox: xlnx,zynqmp-ipi-mailbox:
> Document msg region requirement
>
> Caution: This message originated from an External Source. Use proper caution
> when opening attachments, clicking links, or responding.
>
>
> On Mon, Dec 22, 2025 at 10:16:53AM +0530, Harini T wrote:
> > Add description clarifying that for Versal IPI mailboxes, both host
> > and remote agents must have the "msg" register region defined for
> > successful message passing. Without both, only notification-based
> > communication works.
> >
> > Signed-off-by: Harini T <harini.t@....com>
> > ---
> >  .../bindings/mailbox/xlnx,zynqmp-ipi-mailbox.yaml           | 6 ++++++
> >  1 file changed, 6 insertions(+)
> >
> > diff --git
> > a/Documentation/devicetree/bindings/mailbox/xlnx,zynqmp-ipi-mailbox.ya
> > ml
> > b/Documentation/devicetree/bindings/mailbox/xlnx,zynqmp-ipi-mailbox.ya
> > ml index 04d6473d666f..8fdf77c7935c 100644
> > ---
> > a/Documentation/devicetree/bindings/mailbox/xlnx,zynqmp-ipi-mailbox.ya
> > ml
> > +++ b/Documentation/devicetree/bindings/mailbox/xlnx,zynqmp-ipi-mailbo
> > +++ x.yaml
> > @@ -165,6 +165,12 @@ allOf:
> >          reg-names: false
> >
> >      else:
> > +      description:
>
> Else block cannot have description.

Can I remove the description from else block and move the clarifying text to the top-level description field?

>
> > +        For Versal IPI mailboxes, the "msg" register region is optional.
>
> So it is optional...

The schema marks "msg" as optional to support both notification-only and message-passing use-cases. In hardware, some mailbox channels may be designed for notification only (no buffer), while others support full message passing (with buffer). The schema allows both, but for message passing, "msg" is required on both ends

>
> > +        However, for successful message passing via mailbox, both the
> > + host IPI
>
> And it is not optional. If nothing works, then it is not optional.
>
> And why would it be optional in the first place? You generate your same IP
> with different settings?

There are 2 types of IPI channels (Buffered and Buffer-less)
Some IPI channels are used only for notification (no message buffer, so "msg" is omitted).
Others are used for message passing (buffer present, so "msg" is required).
Reference: https://docs.amd.com/r/en-US/am026-versal-ai-edge-prime-gen2-trm/Features?tocId=K2dUHSdNOkFPpbvkR5v6bQ

>
> Best regards,
> Krzysztof

Thanks,
Harini T