linux-kernel - [PATCH v3 1/3] cacheinfo: Set cache 'id' based on DT data

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Message-Id: <20250711182743.30141-2-james.morse@arm.com>
Date: Fri, 11 Jul 2025 18:27:41 +0000
From: James Morse <james.morse@....com>
To: linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"Rafael J . Wysocki" <rafael@...nel.org>,
	sudeep.holla@....com,
	Rob Herring <robh@...nel.org>,
	Ben Horgan <ben.horgan@....com>,
	Jonathan Cameron <jonathan.cameron@...wei.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>,
	James Morse <james.morse@....com>,
	Gavin Shan <gshan@...hat.com>
Subject: [PATCH v3 1/3] cacheinfo: Set cache 'id' based on DT data

From: Rob Herring <robh@...nel.org>

Use the minimum CPU h/w id of the CPUs associated with the cache for the
cache 'id'. This will provide a stable id value for a given system. As
we need to check all possible CPUs, we can't use the shared_cpu_map
which is just online CPUs. As there's not a cache to CPUs mapping in DT,
we have to walk all CPU nodes and then walk cache levels.

The cache_id exposed to user-space has historically been 32 bits, and
is too late to change. This value is parsed into a u32 by user-space
libraries such as libvirt:
https://github.com/libvirt/libvirt/blob/master/src/util/virresctrl.c#L1588

Give up on assigning cache-id's if a CPU h/w id greater than 32 bits
is found.

match_cache_node() does not make use of the __free() cleanup helpers
because of_find_next_cache_node(prev) does not drop a reference to prev,
and its too easy to accidentally drop the reference on cpu, which belongs
to for_each_of_cpu_node().

Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>
Signed-off-by: Rob Herring <robh@...nel.org>
[ ben: converted to use the __free cleanup idiom ]
Signed-off-by: Ben Horgan <ben.horgan@....com>
[ morse: Add checks to give up if a value larger than 32 bits is seen. ]
Signed-off-by: James Morse <james.morse@....com>
Reviewed-by: Jonathan Cameron <jonathan.cameron@...wei.com>
Reviewed-by: Gavin Shan <gshan@...hat.com>
---
Use as a 32bit value has also been seen in DPDK patches here:
http://inbox.dpdk.org/dev/20241021015246.304431-2-wathsala.vithanage@arm.com/

Changes since v2:
 * Removed broken use of cleanup in the match helper

Changes since v1:
 * Remove the second loop in favour of a helper.
---
 drivers/base/cacheinfo.c | 45 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 45 insertions(+)

diff --git a/drivers/base/cacheinfo.c b/drivers/base/cacheinfo.c
index cf0d455209d7..4e2f60c85e74 100644
--- a/drivers/base/cacheinfo.c
+++ b/drivers/base/cacheinfo.c
@@ -8,6 +8,7 @@
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 
 #include <linux/acpi.h>
+#include <linux/bitfield.h>
 #include <linux/bitops.h>
 #include <linux/cacheinfo.h>
 #include <linux/compiler.h>
@@ -183,6 +184,49 @@ static bool cache_node_is_unified(struct cacheinfo *this_leaf,
 	return of_property_read_bool(np, "cache-unified");
 }
 
+static bool match_cache_node(struct device_node *cpu,
+			     const struct device_node *cache_node)
+{
+	struct device_node *prev, *cache = of_find_next_cache_node(cpu);
+
+	while (cache) {
+		if (cache == cache_node) {
+			of_node_put(cache);
+			return true;
+		}
+
+		prev = cache;
+		cache = of_find_next_cache_node(cache);
+		of_node_put(prev);
+	}
+
+	return false;
+}
+
+static void cache_of_set_id(struct cacheinfo *this_leaf,
+			    struct device_node *cache_node)
+{
+	struct device_node *cpu;
+	u32 min_id = ~0;
+
+	for_each_of_cpu_node(cpu) {
+		u64 id = of_get_cpu_hwid(cpu, 0);
+
+		if (FIELD_GET(GENMASK_ULL(63, 32), id)) {
+			of_node_put(cpu);
+			return;
+		}
+
+		if (match_cache_node(cpu, cache_node))
+			min_id = min(min_id, id);
+	}
+
+	if (min_id != ~0) {
+		this_leaf->id = min_id;
+		this_leaf->attributes |= CACHE_ID;
+	}
+}
+
 static void cache_of_set_props(struct cacheinfo *this_leaf,
 			       struct device_node *np)
 {
@@ -198,6 +242,7 @@ static void cache_of_set_props(struct cacheinfo *this_leaf,
 	cache_get_line_size(this_leaf, np);
 	cache_nr_sets(this_leaf, np);
 	cache_associativity(this_leaf);
+	cache_of_set_id(this_leaf, np);
 }
 
 static int cache_setup_of_node(unsigned int cpu)
-- 
2.39.5