FAILED: patch "[PATCH] ARM: 9522/1: cacheinfo: guard the CLIDR read in populate_cache_leaves()" failed to apply to 6.1-stable tree

[Sasha Levin <sashal@kernel.org>]

The patch below does not apply to the 6.1-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.1.y
git checkout FETCH_HEAD
git cherry-pick -x 2315f2c46e0813d010e7b3ea40f2769621453e27
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '20261107054853-failed-6.1-2315f2c46e08@kernel.org' --subject-prefix 'PATCH 6.1.y' 'HEAD^..'

Thanks,
Sasha

------------------ original commit in Linus's tree ------------------

From 2315f2c46e0813d010e7b3ea40f2769621453e27 Mon Sep 17 00:00:00 2001
From: Karl Mehltretter <kmehltretter@gmail.com>
Date: Mon, 21 Sep 2026 21:45:20 +0100
Subject: [PATCH] ARM: 9522/1: cacheinfo: guard the CLIDR read in
 populate_cache_leaves()

ARM1176 and ARM11 MPCore can be reported as ARMv7 by
cpu_architecture() even though they lack CLIDR. populate_cache_leaves()
therefore needs the CTR-format check used by detect_cache_level().

DT-based early allocation bypasses init_cache_level(), so its check
no longer protects populate_cache_leaves(). A combined ARMv6/ARMv7
SMP kernel can reach this path on BCM2835, whose DT describes its
caches.

Share the CLIDR capability check between detection and population.
Return -ENOENT from population when CLIDR is unavailable, preserving
the existing absence of cacheinfo and avoiding a new topology warning.

Assisted-by: LLM

Cc: stable@vger.kernel.org
Tested-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Link: https://lore.kernel.org/r/20260912195552.76673-4-kmehltretter@gmail.com/
Signed-off-by: Karl Mehltretter <kmehltretter@gmail.com>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
---
 arch/arm/kernel/cacheinfo.c | 25 +++++++++++++------------
 1 file changed, 13 insertions(+), 12 deletions(-)

diff --git a/arch/arm/kernel/cacheinfo.c b/arch/arm/kernel/cacheinfo.c
index 31591c9472548..993c8a1347860 100644
--- a/arch/arm/kernel/cacheinfo.c
+++ b/arch/arm/kernel/cacheinfo.c
@@ -80,19 +80,21 @@ static void ci_leaf_init(struct cacheinfo *this_leaf,
 	this_leaf->type = type;
 }
 
-static int detect_cache_level(unsigned int *level_p, unsigned int *leaves_p)
+static bool clidr_present(void)
 {
-	unsigned int ctype, level, leaves;
-	u32 ctr, format;
-
 	/* CLIDR is not present before ARMv7/v7m */
 	if (cpu_architecture() < CPU_ARCH_ARMv7)
-		return -EOPNOTSUPP;
+		return false;
 
 	/* Don't try reading CLIDR if CTR declares old format */
-	ctr = read_cpuid_cachetype();
-	format = FIELD_GET(CTR_FORMAT_MASK, ctr);
-	if (format != CTR_FORMAT_ARMV7)
+	return FIELD_GET(CTR_FORMAT_MASK, read_cpuid_cachetype()) == CTR_FORMAT_ARMV7;
+}
+
+static int detect_cache_level(unsigned int *level_p, unsigned int *leaves_p)
+{
+	unsigned int ctype, level, leaves;
+
+	if (!clidr_present())
 		return -EOPNOTSUPP;
 
 	for (level = 1, leaves = 0; level <= MAX_CACHE_LEVEL; level++) {
@@ -150,11 +152,10 @@ int populate_cache_leaves(unsigned int cpu)
 	enum cache_type type;
 	struct cpu_cacheinfo *this_cpu_ci = get_cpu_cacheinfo(cpu);
 	struct cacheinfo *infos = this_cpu_ci->info_list;
-	unsigned int arch = cpu_architecture();
 
-	/* CLIDR is not present before ARMv7/v7m */
-	if (arch < CPU_ARCH_ARMv7)
-		return -EOPNOTSUPP;
+	/* The device tree can describe caches CLIDR cannot fill in. */
+	if (!clidr_present())
+		return -ENOENT;
 
 	for (idx = 0, level = 1; level <= this_cpu_ci->num_levels &&
 	     idx < this_cpu_ci->num_leaves; level++) {
-- 
2.53.0