FAILED: patch "[PATCH] ARM: 9521/1: cacheinfo: count external caches in early_cache_level()" failed to apply to 6.6-stable tree

The patch below does not apply to the 6.6-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 <[email protected]>.

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-6.6.y
git checkout FETCH_HEAD
git cherry-pick -x 4fd69e8a9ebc42e292637ec2ebfb6bcf2d2f6c0e
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '[email protected]' --subject-prefix 'PATCH 6.6.y' 'HEAD^..'

Thanks,
Sasha

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

From 4fd69e8a9ebc42e292637ec2ebfb6bcf2d2f6c0e Mon Sep 17 00:00:00 2001
From: Karl Mehltretter <[email protected]>
Date: Mon, 21 Sep 2026 21:44:33 +0100
Subject: [PATCH] ARM: 9521/1: cacheinfo: count external caches in
early_cache_level()

early_cache_level() counts only caches described by CLIDR. An external PL310 is absent from CLIDR, and its arm,pl310-cache compatible is not accepted by init_of_cache_level(), so early allocation falls back to an incomplete count. init_cache_level() later adds the DT-described L2, forcing reallocation on the secondary CPU with interrupts disabled. This defeats early allocation on PREEMPT_RT.

Use init_cache_level() for early sizing too, so the initial allocation includes external caches described by the device tree.

---
 arch/arm/kernel/cacheinfo.c | 12 +++++-------
 1 file changed, 5 insertions(+), 7 deletions(-)

index 860eeb03cfe5d..31591c9472548 100644
@@ -111,13 +111,6 @@ static int detect_cache_level(unsigned int *level_p, unsigned int *leaves_p)
 	return 0;
 }
 
-int early_cache_level(unsigned int cpu)
-{
-	struct cpu_cacheinfo *this_cpu_ci = get_cpu_cacheinfo(cpu);
-
-	return detect_cache_level(&this_cpu_ci->num_levels, &this_cpu_ci->num_leaves);
-}
-
 int init_cache_level(unsigned int cpu)
 {
 	unsigned int level, leaves;

@@ -146,6 +139,11 @@ int init_cache_level(unsigned int cpu)
 	return 0;
 }
 
+int early_cache_level(unsigned int cpu)
+{
+	return init_cache_level(cpu);
+}
+
 int populate_cache_leaves(unsigned int cpu)
 {
 	unsigned int level, idx;

2.53.0