linux-kernel - Re: [PATCH v10 07/15] dt-bindings: interrupt-controller: Add RISC-V incoming MSI controller

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Message-ID: <20231013-pluck-skies-1b4ee57e770c@spud>
Date:   Fri, 13 Oct 2023 08:41:10 +0100
From:   Conor Dooley <conor@...nel.org>
To:     Anup Patel <apatel@...tanamicro.com>
Cc:     Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Marc Zyngier <maz@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Frank Rowand <frowand.list@...il.com>,
        Conor Dooley <conor+dt@...nel.org>,
        Atish Patra <atishp@...shpatra.org>,
        Andrew Jones <ajones@...tanamicro.com>,
        Sunil V L <sunilvl@...tanamicro.com>,
        Saravana Kannan <saravanak@...gle.com>,
        Anup Patel <anup@...infault.org>,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org,
        Conor Dooley <conor.dooley@...rochip.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Subject: Re: [PATCH v10 07/15] dt-bindings: interrupt-controller: Add RISC-V
 incoming MSI controller

Hey Anup,

On Fri, Oct 13, 2023 at 12:16:45PM +0530, Anup Patel wrote:
> On Thu, Oct 12, 2023 at 10:05 PM Conor Dooley <conor@...nel.org> wrote:
> > On Tue, Oct 03, 2023 at 10:13:55AM +0530, Anup Patel wrote:
> > > We add DT bindings document for the RISC-V incoming MSI controller
> > > (IMSIC) defined by the RISC-V advanced interrupt architecture (AIA)
> > > specification.
> > >
> > > Signed-off-by: Anup Patel <apatel@...tanamicro.com>
> > > Reviewed-by: Conor Dooley <conor.dooley@...rochip.com>
> >
> > Just FYI, since they'll reply to this themselves, but some of the
> > Microchip folks have run into problems with sparse hart indexes while
> > trying to use the imsic binding to describe some configurations they
> > have. I think there were also so problems with how to describe to a
> > linux guest which file to use, when the first hart available to the
> > guest does not use the first file. They'll do a better job of describing
> > their problems than I will, so I shall leave it to them!
> 
> Quoting AIA spec:
> "For the purpose of locating the memory pages of interrupt files in the
> address space, assume each hart (or each hart within a group) has a
> unique hart number that may or may not be related to the unique hart
> identifiers (“hart IDs”) that the RISC-V Privileged Architecture assigns
> to harts."
> 
> It is very easy to get confused between the AIA "hart index" and
> "hart IDs" defined by the RISC-V Privileged specification but these
> are two very different things. The AIA "hart index" over here is the
> bits in the address of an IMSIC file.
> 
> This DT binding follows the IMSIC file arrangement in the address
> space as defined by the section "3.6 Arrangement of the memory
> regions of multiple interrupt files" of the AIA specification. This
> arrangement is MANDATORY for platforms having both APLIC
> and IMSIC because in MSI-mode the APLIC generates target
> MSI address based the IMSIC file arrangement described in the
> section "3.6 Arrangement of the memory regions of multiple
> interrupt files". In fact, this also applies to virtual platforms
> created by hypervisors (KVM, Xen, ...)

Thanks for pointing this out - I'll pass it on and hopefully it is
helpful to them. If not, I expect that you'll hear :)

Cheers,
Conor.

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