irqchip/gic-v3: Enable non-coherent redistributors/ITSes DT probing

The GIC architecture specification defines a set of registers
for redistributors and ITSes that control the sharebility and
cacheability attributes of redistributors/ITSes initiator ports
on the interconnect (GICR_[V]PROPBASER, GICR_[V]PENDBASER,
GITS_BASER<n>).

Architecturally the GIC provides a means to drive shareability
and cacheability attributes signals and related IWB/OWB/ISH barriers
but it is not mandatory for designs to wire up the corresponding
interconnect signals that control the cacheability/shareability
of transactions.

Redistributors and ITSes interconnect ports can be connected to
non-coherent interconnects that are not able to manage the
shareability/cacheability attributes; this implicitly makes
the redistributors and ITSes non-coherent observers.

So far, the GIC driver on probe executes a write to "probe" for
the redistributors and ITSes registers shareability bitfields
by writing a value (ie InnerShareable - the shareability domain the
CPUs are in) and check it back to detect whether the value sticks or
not; this hinges on a GIC programming model behaviour that predates the
current specifications, that just define shareability bits as writeable
but do not guarantee that writing certain shareability values
enable the expected behaviour for the redistributors/ITSes
memory interconnect ports.

To enable non-coherent GIC designs, introduce the "dma-noncoherent"
device tree property to allow firmware to describe redistributors and
ITSes as non-coherent observers on the memory interconnect and use the
property to force the shareability attributes to be programmed into the
redistributors and ITSes registers through the GIC quirks mechanism.

Signed-off-by: Lorenzo Pieralisi <lpieralisi@kernel.org>
Cc: Robin Murphy <robin.murphy@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Marc Zyngier <maz@kernel.org>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20231006125929.48591-3-lpieralisi@kernel.org

1 files changed, 13 insertions, 0 deletions

diff --git a/drivers/irqchip/irq-gic-v3.c b/drivers/irqchip/irq-gic-v3.c
index eedfa8e9f077..f59ac9586b7b 100644
--- a/drivers/irqchip/irq-gic-v3.c
+++ b/drivers/irqchip/irq-gic-v3.c
@@ -1857,6 +1857,14 @@ static bool gic_enable_quirk_arm64_2941627(void *data)
 	return true;
 }
 
+static bool rd_set_non_coherent(void *data)
+{
+	struct gic_chip_data *d = data;
+
+	d->rdists.flags |= RDIST_FLAGS_FORCE_NON_SHAREABLE;
+	return true;
+}
+
 static const struct gic_quirk gic_quirks[] = {
 	{
 		.desc	= "GICv3: Qualcomm MSM8996 broken firmware",
@@ -1924,6 +1932,11 @@ static const struct gic_quirk gic_quirks[] = {
 		.init	= gic_enable_quirk_arm64_2941627,
 	},
 	{
+		.desc   = "GICv3: non-coherent attribute",
+		.property = "dma-noncoherent",
+		.init   = rd_set_non_coherent,
+	},
+	{
 	}
 };