[RFC PATCH 2/2] arm64: mm: add SMCCC-backed cache invalidate provider

[Srirangan Madhavan <smadhavan@nvidia.com>]

Add an arm64 cache maintenance backend that discovers SMCCC cache
clean+invalidate support, queries attributes, handles transient BUSY and
RATE_LIMITED responses with bounded retries, and registers with the generic
cache coherency framework.

Signed-off-by: Srirangan Madhavan <smadhavan@nvidia.com>
---
 MAINTAINERS                 |   1 +
 arch/arm64/mm/Makefile      |   1 +
 arch/arm64/mm/cache_maint.c | 180 ++++++++++++++++++++++++++++++++++++
 3 files changed, 182 insertions(+)
 create mode 100644 arch/arm64/mm/cache_maint.c

diff --git a/MAINTAINERS b/MAINTAINERS
index 2fb1c75afd16..33c35f8e6e40 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -25383,6 +25383,7 @@ M:	Jonathan Cameron <jic23@kernel.org>
 S:	Maintained
 T:	git https://git.kernel.org/pub/scm/linux/kernel/git/conor/linux.git/
 F:	Documentation/devicetree/bindings/cache/
+F:	arch/arm64/mm/cache_maint.c
 F:	drivers/cache
 F:	include/linux/cache_coherency.h
 F:	lib/cache_maint.c
diff --git a/arch/arm64/mm/Makefile b/arch/arm64/mm/Makefile
index c26489cf96cd..b247dc5dfd45 100644
--- a/arch/arm64/mm/Makefile
+++ b/arch/arm64/mm/Makefile
@@ -12,6 +12,7 @@ obj-$(CONFIG_TRANS_TABLE)	+= trans_pgd-asm.o
 obj-$(CONFIG_DEBUG_VIRTUAL)	+= physaddr.o
 obj-$(CONFIG_ARM64_MTE)		+= mteswap.o
 obj-$(CONFIG_ARM64_GCS)		+= gcs.o
+obj-$(CONFIG_ARCH_HAS_CPU_CACHE_INVALIDATE_MEMREGION) += cache_maint.o
 KASAN_SANITIZE_physaddr.o	+= n
 
 obj-$(CONFIG_KASAN)		+= kasan_init.o
diff --git a/arch/arm64/mm/cache_maint.c b/arch/arm64/mm/cache_maint.c
new file mode 100644
index 000000000000..ea7dd30d5dfa
--- /dev/null
+++ b/arch/arm64/mm/cache_maint.c
@@ -0,0 +1,180 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2026 NVIDIA Corporation
+ *
+ * Arm64 cache maintenance provider using SMCCC cache clean+invalidate calls.
+ */
+
+#include <linux/arm-smccc.h>
+#include <linux/cache_coherency.h>
+#include <linux/cleanup.h>
+#include <linux/delay.h>
+#include <linux/errno.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/mutex.h>
+#include <linux/nmi.h>
+
+#define SMCCC_CACHE_MAX_RETRIES		5
+#define SMCCC_CACHE_MAX_DELAY_US	20000
+
+/* DEN0028 v1.7: bit[0] == 1 means implementation flushes all caches globally */
+#define SMCCC_CACHE_ATTR_GLOBAL_OP	BIT(0)
+
+struct arm64_smccc_cache {
+	/* Must be first member */
+	struct cache_coherency_ops_inst cci;
+	struct mutex lock; /* Serializes SMCCC cache maintenance calls. */
+	u32 latency_us;
+	u32 rate_limit;
+	bool global_op;
+	u64 global_flush_gen;
+};
+
+static struct arm64_smccc_cache *arm64_smccc_cache;
+
+static int smccc_cache_status_to_errno(s32 status)
+{
+	switch (status) {
+	case SMCCC_RET_SUCCESS:
+		return 0;
+	case SMCCC_RET_NOT_SUPPORTED:
+	case SMCCC_RET_NOT_REQUIRED:
+		return -EOPNOTSUPP;
+	case SMCCC_RET_INVALID_PARAMETER:
+		return -EINVAL;
+	case SMCCC_RET_RATE_LIMITED:
+		return -EAGAIN;
+	case SMCCC_RET_BUSY:
+		return -EBUSY;
+	default:
+		return -EIO;
+	}
+}
+
+static int smccc_cache_delay_us(const struct arm64_smccc_cache *cache)
+{
+	u64 delay_us = 0;
+
+	if (cache->rate_limit)
+		delay_us = DIV_ROUND_UP_ULL(USEC_PER_SEC, cache->rate_limit);
+
+	if (cache->latency_us)
+		delay_us = max_t(u64, delay_us, cache->latency_us);
+
+	if (!delay_us)
+		delay_us = 1000;
+
+	return min_t(u64, delay_us, SMCCC_CACHE_MAX_DELAY_US);
+}
+
+static int arm64_smccc_cache_wbinv(struct cache_coherency_ops_inst *cci,
+				   struct cc_inval_params *invp)
+{
+	struct arm64_smccc_cache *cache =
+		container_of(cci, struct arm64_smccc_cache, cci);
+	struct arm_smccc_res res = {};
+	int delay_us = smccc_cache_delay_us(cache);
+	u64 gen = 0;
+	s32 status;
+	int ret;
+	int i;
+
+	if (!invp->size)
+		return -EINVAL;
+
+	if (cache->global_op)
+		gen = READ_ONCE(cache->global_flush_gen);
+
+	guard(mutex)(&cache->lock);
+
+	/*
+	 * If firmware reports a global operation type, a successful operation
+	 * covers every request that was already waiting behind it. Skip if the
+	 * generation advanced while this request was waiting to enter the
+	 * serialized firmware call path.
+	 */
+	if (cache->global_op && gen != READ_ONCE(cache->global_flush_gen))
+		return 0;
+
+	for (i = 0; i < SMCCC_CACHE_MAX_RETRIES; i++) {
+		/* Long firmware operations can trigger watchdog checks. */
+		touch_nmi_watchdog();
+
+		arm_smccc_1_1_invoke(ARM_SMCCC_ARCH_CLEAN_INV_MEMREGION,
+				     invp->addr, invp->size, 0UL, &res);
+		status = (s32)res.a0;
+		ret = smccc_cache_status_to_errno(status);
+		if (!ret) {
+			if (cache->global_op) {
+				WRITE_ONCE(cache->global_flush_gen,
+					   cache->global_flush_gen + 1);
+			}
+			return 0;
+		}
+
+		if (ret != -EBUSY && ret != -EAGAIN)
+			return ret;
+
+		usleep_range(delay_us, delay_us + 100);
+	}
+
+	return -EBUSY;
+}
+
+static const struct cache_coherency_ops arm64_smccc_cache_ops = {
+	.wbinv = arm64_smccc_cache_wbinv,
+};
+
+static int __init arm64_smccc_cache_init(void)
+{
+	struct arm_smccc_res res = {};
+	s32 status;
+	int ret;
+
+	if (arm_smccc_get_version() < ARM_SMCCC_VERSION_1_1)
+		return -ENODEV;
+
+	if (arm_smccc_1_1_get_conduit() == SMCCC_CONDUIT_NONE)
+		return -ENODEV;
+
+	arm_smccc_1_1_invoke(ARM_SMCCC_ARCH_FEATURES_FUNC_ID,
+			     ARM_SMCCC_ARCH_CLEAN_INV_MEMREGION, &res);
+	status = (s32)res.a0;
+	if (status < 0)
+		return -ENODEV;
+
+	arm_smccc_1_1_invoke(ARM_SMCCC_ARCH_FEATURES_FUNC_ID,
+			     ARM_SMCCC_ARCH_CLEAN_INV_MEMREGION_ATTRIBUTES, &res);
+	status = (s32)res.a0;
+	if (status < 0)
+		return -ENODEV;
+
+	arm_smccc_1_1_invoke(ARM_SMCCC_ARCH_CLEAN_INV_MEMREGION_ATTRIBUTES, &res);
+	status = (s32)res.a0;
+	if (status)
+		return -ENODEV;
+
+	arm64_smccc_cache =
+		cache_coherency_ops_instance_alloc(&arm64_smccc_cache_ops,
+						   struct arm64_smccc_cache,
+						   cci);
+	if (!arm64_smccc_cache)
+		return -ENOMEM;
+
+	mutex_init(&arm64_smccc_cache->lock);
+	arm64_smccc_cache->latency_us = lower_32_bits(res.a2);
+	arm64_smccc_cache->rate_limit = lower_32_bits(res.a3);
+	arm64_smccc_cache->global_op = !!(res.a1 & SMCCC_CACHE_ATTR_GLOBAL_OP);
+
+	ret = cache_coherency_ops_instance_register(&arm64_smccc_cache->cci);
+	if (ret) {
+		cache_coherency_ops_instance_put(&arm64_smccc_cache->cci);
+		arm64_smccc_cache = NULL;
+		return ret;
+	}
+
+	pr_info("SMCCC cache clean+invalidate provider registered\n");
+	return 0;
+}
+arch_initcall(arm64_smccc_cache_init);
-- 
2.43.0