linux-kernel - Re: [PATCH v2 07/17] irqchip/gic: Atomically update affinity

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Date:   Sat, 11 Sep 2021 11:49:20 +0900
From:   Magnus Damm <magnus.damm@...il.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Marc Zyngier <maz@...nel.org>,
        Russell King <linux@....linux.org.uk>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Will Deacon <will@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        Sumit Garg <sumit.garg@...aro.org>,
        Valentin Schneider <Valentin.Schneider@....com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Gregory Clement <gregory.clement@...tlin.com>,
        Andrew Lunn <andrew@...n.ch>,
        Android Kernel Team <kernel-team@...roid.com>,
        stable <stable@...r.kernel.org>,
        Magnus Damm <damm+renesas@...nsource.se>,
        Niklas Söderlund 
        <niklas.soderlund+renesas@...natech.se>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>
Subject: Re: [PATCH v2 07/17] irqchip/gic: Atomically update affinity

Hi Geert, Mark, RMK, everyone,

Thanks for your efforts. Let me just chime in with a few details and a question.

On Fri, Sep 10, 2021 at 10:19 PM Geert Uytterhoeven
<geert@...ux-m68k.org> wrote:
> On Fri, Sep 10, 2021 at 12:23 PM Marc Zyngier <maz@...nel.org> wrote:
> > On Thu, 09 Sep 2021 16:22:01 +0100,
> > Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
>     GIC: enabling workaround for broken byte access

Indeed, byte access is unsupported according to the EMEV2 documentation.

The EMEV2 documentation R19UH0036EJ0600 Chapter 7 Interrupt Control on
page 97 says:
"Interrupt registers can be accessed via the APB bus, in 32-bit units"
"For details about register functions, see ARM Generic Interrupt
Controller Architecture Specification Architecture version 1.0"
The file  "R19UH0036EJ0600_1Chip.pdf" is the 6th edition version
published in 2010 and is not marked as confidential.

>From my basic research, "ARM Generic Interrupt Controller Architecture
Specification Architecture version 1.0" is documented in ARM IHI 0048A
from 2008 (Non-Confidential) which contains:
"All GIC registers are 32-bit wide." and "All registers support 32-bit
word access..."
"In addition, the following registers support byte accesses:"
"ICDIPR"
"ICDIPTR"

So the GICv1 documentation says byte access is partially supported
however EMEV2 documentation says 32-bit access is required.

> > +               .compatible     = "arm,pl390",
> > +               .init           = gic_enable_rmw_access,
> > +       },

May I ask about a clarification about the EMEV2 DTS and DT binding
documentation in:
arch/arm/boot/dts/emev2.dts
Documentation/devicetree/bindings/interrupt-controller/arm,gic.yaml

On EMEV2 the DT compatible string currently seems to be the rather
generic "arm,pl390". In the DT binding documentation GICv1 is listed
in an example as "arm,cortex-a9-gic". Is there any reason for not
using the GICv1 compatible string (and 32-bit access) for EMEV2? Just
curious.

Cheers,

/ magnus