linux-kernel - [PATCH 0/2] irqchip/gic-v3: Enable non-coherent GIC designs probing

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Message-Id: <20230905104721.52199-1-lpieralisi@kernel.org>
Date:   Tue,  5 Sep 2023 12:47:19 +0200
From:   Lorenzo Pieralisi <lpieralisi@...nel.org>
To:     linux-kernel@...r.kernel.org
Cc:     Lorenzo Pieralisi <lpieralisi@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
        Mark Rutland <mark.rutland@....com>,
        Robin Murphy <robin.murphy@....com>,
        Rob Herring <robh+dt@...nel.org>,
        Fang Xiang <fangxiang3@...omi.com>,
        Marc Zyngier <maz@...nel.org>
Subject: [PATCH 0/2] irqchip/gic-v3: Enable non-coherent GIC designs probing

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 (2):
  dt-bindings: interrupt-controller: arm,gic-v3: Add dma-noncoherent
    property
  irqchip/gic-v3: Enable non-coherent redistributors/ITSes probing

 .../interrupt-controller/arm,gic-v3.yaml      |  8 ++++++++
 drivers/irqchip/irq-gic-v3-its.c              | 19 +++++++++++++++----
 2 files changed, 23 insertions(+), 4 deletions(-)

-- 
2.34.1