linux-kernel - [PATCH v2] of: property: fw_devlink: Do not use interrupt-parent directly

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Message-ID: <20241120233124.3649382-1-samuel.holland@sifive.com>
Date: Wed, 20 Nov 2024 15:31:16 -0800
From: Samuel Holland <samuel.holland@...ive.com>
To: Rob Herring <robh@...nel.org>,
	Saravana Kannan <saravanak@...gle.com>
Cc: Anup Patel <apatel@...tanamicro.com>,
	Samuel Holland <samuel.holland@...ive.com>,
	Marc Zyngier <maz@...nel.org>,
	stable@...r.kernel.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Linus Walleij <linus.walleij@...aro.org>,
	Thierry Reding <treding@...dia.com>,
	devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH v2] of: property: fw_devlink: Do not use interrupt-parent directly

commit 7f00be96f125 ("of: property: Add device link support for
interrupt-parent, dmas and -gpio(s)") started adding device links for
the interrupt-parent property. commit 4104ca776ba3 ("of: property: Add
fw_devlink support for interrupts") and commit f265f06af194 ("of:
property: Fix fw_devlink handling of interrupts/interrupts-extended")
later added full support for parsing the interrupts and
interrupts-extended properties, which includes looking up the node of
the parent domain. This made the handler for the interrupt-parent
property redundant.

In fact, creating device links based solely on interrupt-parent is
problematic, because it can create spurious cycles. A node may have
this property without itself being an interrupt controller or consumer.
For example, this property is often present in the root node or a /soc
bus node to set the default interrupt parent for child nodes. However,
it is incorrect for the bus to depend on the interrupt controller, as
some of the bus's children may not be interrupt consumers at all or may
have a different interrupt parent.

Resolving these spurious dependency cycles can cause an incorrect probe
order for interrupt controller drivers. This was observed on a RISC-V
system with both an APLIC and IMSIC under /soc, where interrupt-parent
in /soc points to the APLIC, and the APLIC msi-parent points to the
IMSIC. fw_devlink found three dependency cycles and attempted to probe
the APLIC before the IMSIC. After applying this patch, there were no
dependency cycles and the probe order was correct.

Acked-by: Marc Zyngier <maz@...nel.org>
Cc: stable@...r.kernel.org
Fixes: 4104ca776ba3 ("of: property: Add fw_devlink support for interrupts")
Signed-off-by: Samuel Holland <samuel.holland@...ive.com>
---

Changes in v2:
 - Fix typo in commit message
 - Add Fixes: tag and CC stable

 drivers/of/property.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/drivers/of/property.c b/drivers/of/property.c
index 11b922fde7af..7bd8390f2fba 100644
--- a/drivers/of/property.c
+++ b/drivers/of/property.c
@@ -1213,7 +1213,6 @@ DEFINE_SIMPLE_PROP(iommus, "iommus", "#iommu-cells")
 DEFINE_SIMPLE_PROP(mboxes, "mboxes", "#mbox-cells")
 DEFINE_SIMPLE_PROP(io_channels, "io-channels", "#io-channel-cells")
 DEFINE_SIMPLE_PROP(io_backends, "io-backends", "#io-backend-cells")
-DEFINE_SIMPLE_PROP(interrupt_parent, "interrupt-parent", NULL)
 DEFINE_SIMPLE_PROP(dmas, "dmas", "#dma-cells")
 DEFINE_SIMPLE_PROP(power_domains, "power-domains", "#power-domain-cells")
 DEFINE_SIMPLE_PROP(hwlocks, "hwlocks", "#hwlock-cells")
@@ -1359,7 +1358,6 @@ static const struct supplier_bindings of_supplier_bindings[] = {
 	{ .parse_prop = parse_mboxes, },
 	{ .parse_prop = parse_io_channels, },
 	{ .parse_prop = parse_io_backends, },
-	{ .parse_prop = parse_interrupt_parent, },
 	{ .parse_prop = parse_dmas, .optional = true, },
 	{ .parse_prop = parse_power_domains, },
 	{ .parse_prop = parse_hwlocks, },
-- 
2.45.1