linux-kernel - Re: [PATCH v4 01/26] dt-bindings: interrupt-controller: Add Arm GICv5

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Message-ID: <aD6ouVAXy5qcZtM/@lpieralisi>
Date: Tue, 3 Jun 2025 09:48:09 +0200
From: Lorenzo Pieralisi <lpieralisi@...nel.org>
To: Peter Maydell <peter.maydell@...aro.org>, Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>
Cc: Marc Zyngier <maz@...nel.org>, Thomas Gleixner <tglx@...utronix.de>,
	Conor Dooley <conor+dt@...nel.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>, andre.przywara@....com,
	Arnd Bergmann <arnd@...db.de>,
	Sascha Bischoff <sascha.bischoff@....com>,
	Timothy Hayes <timothy.hayes@....com>,
	"Liam R. Howlett" <Liam.Howlett@...cle.com>,
	Mark Rutland <mark.rutland@....com>,
	Jiri Slaby <jirislaby@...nel.org>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	devicetree@...r.kernel.org, suzuki.poulose@....com
Subject: Re: [PATCH v4 01/26] dt-bindings: interrupt-controller: Add Arm GICv5

On Thu, May 29, 2025 at 02:17:26PM +0100, Peter Maydell wrote:
> On Thu, 29 May 2025 at 13:44, Lorenzo Pieralisi <lpieralisi@...nel.org> wrote:
> >
> > [+Andre, Peter]
> >
> > On Tue, May 13, 2025 at 07:47:54PM +0200, Lorenzo Pieralisi wrote:
> > > +      reg:
> > > +        minItems: 1
> > > +        items:
> > > +          - description: IRS control frame
> >
> > I came across it while testing EL3 firmware, raising the topic for
> > discussion.
> >
> > The IRS (and the ITS) has a config frame (need to patch the typo
> > s/control/config, already done) per interrupt domain supported, that is,
> > it can have up to 4 config frames:
> >
> > - EL3
> > - Secure
> > - Realm
> > - Non-Secure
> >
> > The one described in this binding is the non-secure one.
> >
> > IIUC, everything described in the DT represents the non-secure address
> > space.
> 
> The dt bindings do allow for describing Secure-world devices:
> Documentation/devicetree/bindings/arm/secure.txt has the
> details. We use this in QEMU so we can provide a DTB to
> guest EL3 firmware that tells it where the hardware is
> (and which EL3 can then pass on to an NS kernel). It would
> be helpful for the GICv5 binding to be defined in a way that
> we can do this for a GICv5 system too.

It would be good to understand what DT {should/should not} describe and
whether this DT usage to configure firmware is under the DT maintainers
radar or it is an attempt at reusing it to avoid implementing a
configuration scheme.

Rob, Krzysztof,

Any thoughts on the matter please ?

[...]

> The tempting thing to do is to have regs[] list the frames
> in some given order, but the spec makes them not simple
> supersets, allowing all of:
>  * NS
>  * S
>  * NS, S, EL3
>  * NS, Realm, EL3
>  * NS, Realm, S, EL3

Maybe reg-names can help ? Even though first we need to understand
what resources should be described in DT.

Current bindings are reviewed and I am not keen on dragging this
discussion on forever - the information the kernel requires is there,
I'd like to bring this to a close.

Thanks,
Lorenzo

> 
> secure.txt says:
> # The general principle of the naming scheme for Secure world bindings
> # is that any property that needs a different value in the Secure world
> # can be supported by prefixing the property name with "secure-". So for
> # instance "secure-foo" would override "foo".
> 
> So maybe we could have
>  reg : the NS frame(s)
>  secure-reg : the S frame(s)
>  realm-reg : the Realm frame(s)
>  root-reg : the EL3 frame(s)
> 
> ??
> 
> thanks
> -- PMM