linux-kernel - Re: [PATCH v4 0/3] irqchip/gic-v3: Enable non-coherent GIC designs probing

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Message-ID: <86h6jt9vs7.wl-maz@kernel.org>
Date: Thu, 04 Jan 2024 11:34:48 +0000
From: Marc Zyngier <maz@...nel.org>
To: "Rafael J. Wysocki" <rafael@...nel.org>
Cc: Lorenzo Pieralisi <lpieralisi@...nel.org>,
	linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-acpi@...r.kernel.org,
	acpica-devel@...ts.linux.dev,
	Mark Rutland <mark.rutland@....com>,
	Robin Murphy <robin.murphy@....com>,
	Fang Xiang <fangxiang3@...omi.com>,
	Robert Moore <robert.moore@...el.com>
Subject: Re: [PATCH v4 0/3] irqchip/gic-v3: Enable non-coherent GIC designs probing

On Wed, 03 Jan 2024 13:43:16 +0000,
"Rafael J. Wysocki" <rafael@...nel.org> wrote:
> 
> On Wed, Dec 27, 2023 at 12:00 PM Lorenzo Pieralisi
> <lpieralisi@...nel.org> wrote:
> >
> > This series is v4 of previous series:
> >
> > v3: https://lore.kernel.org/all/20231006125929.48591-1-lpieralisi@kernel.org
> > v2: https://lore.kernel.org/all/20230906094139.16032-1-lpieralisi@kernel.org
> > v1: https://lore.kernel.org/all/20230905104721.52199-1-lpieralisi@kernel.org
> >
> > v3 -> v4:
> >         - Dropped patches [1-3], already merged
> >         - Added Linuxized ACPICA changes accepted upstream
> >         - Rebased against v6.7-rc3
> >
> > v2 -> v3:
> >         - Added ACPICA temporary changes and ACPI changes to implement
> >           ECR https://bugzilla.tianocore.org/show_bug.cgi?id=4557
> >         - ACPI changes are for testing purposes - subject to ECR code
> >           first approval
> >
> > v1 -> v2:
> >         - Updated DT bindings as per feedback
> >         - Updated patch[2] to use GIC quirks infrastructure
> >
> > Original cover letter
> > ---
> > The GICv3 architecture specifications provide a means for the
> > system programmer to set the shareability and cacheability
> > attributes the GIC components (redistributors and ITSes) use
> > to drive memory transactions.
> >
> > Albeit the architecture give control over shareability/cacheability
> > memory transactions attributes (and barriers), it is allowed to
> > connect the GIC interconnect ports to non-coherent memory ports
> > on the interconnect, basically tying off shareability/cacheability
> > "wires" and de-facto making the redistributors and ITSes non-coherent
> > memory observers.
> >
> > This series aims at starting a discussion over a possible solution
> > to this problem, by adding to the GIC device tree bindings the
> > standard dma-noncoherent property. The GIC driver uses the property
> > to force the redistributors and ITSes shareability attributes to
> > non-shareable, which consequently forces the driver to use CMOs
> > on GIC memory tables.
> >
> > On ARM DT DMA is default non-coherent, so the GIC driver can't rely
> > on the generic DT dma-coherent/non-coherent property management layer
> > (of_dma_is_coherent()) which would default all GIC designs in the field
> > as non-coherent; it has to rely on ad-hoc dma-noncoherent property handling.
> >
> > When a consistent approach is agreed upon for DT an equivalent binding will
> > be put forward for ACPI based systems.
> >
> > Lorenzo Pieralisi (3):
> >   ACPICA: MADT: Add GICC online capable bit handling
> >   ACPICA: MADT: Add new MADT GICC/GICR/ITS non-coherent flags handling
> >   irqchip/gic-v3: Enable non-coherent redistributors/ITSes ACPI probing
> >
> >  drivers/acpi/processor_core.c    | 21 +++++++++++++++++++++
> >  drivers/irqchip/irq-gic-common.h |  8 ++++++++
> >  drivers/irqchip/irq-gic-v3-its.c |  4 ++++
> >  drivers/irqchip/irq-gic-v3.c     |  9 +++++++++
> >  include/acpi/actbl2.h            | 12 ++++++++++--
> >  include/linux/acpi.h             |  3 +++
> >  6 files changed, 55 insertions(+), 2 deletions(-)
> >
> > --
> 
> I can apply the first 2 patches, but I would need an ACK for the 3rd one.
> 
> Alternatively, feel free to add
> 
> Acked-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> 
> to the first 2 patches and route them via ARM64.

Thanks for that. I have some comments on the third patch, which I'd
like to see addressed beforehand. This is probably all 6.9 material
anyway (nobody is affected by this so far).

	M.

-- 
Without deviation from the norm, progress is not possible.