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

[Magnus Damm <magnus.damm@gmail.com>]

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@linux-m68k.org> wrote:
> On Fri, Sep 10, 2021 at 12:23 PM Marc Zyngier <maz@kernel.org> wrote:
> > On Thu, 09 Sep 2021 16:22:01 +0100,
> > Geert Uytterhoeven <geert@linux-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