Probing MPAM is convoluted. MSCs that are integrated with a CPU may
only be accessible from those CPUs, and they may not be online.
Touching the hardware early is pointless as MPAM can't be used until
the system-wide common values for num_partid and num_pmg have been
discovered.

Start with driver probe/remove and mapping the MSC.

CC: Carl Worth <redacted>
Signed-off-by: James Morse <james.morse@arm.com>
---
Changes since RFC:
 * Check for status=broken DT devices.
 * Moved all the files around.
 * Made Kconfig symbols depend on EXPERT
---
 arch/arm64/Kconfig              |   1 +
 drivers/Kconfig                 |   2 +
 drivers/Makefile                |   1 +
 drivers/resctrl/Kconfig         |  11 ++
 drivers/resctrl/Makefile        |   4 +
 drivers/resctrl/mpam_devices.c  | 336 ++++++++++++++++++++++++++++++++
 drivers/resctrl/mpam_internal.h |  62 ++++++
 7 files changed, 417 insertions(+)
 create mode 100644 drivers/resctrl/Kconfig
 create mode 100644 drivers/resctrl/Makefile
 create mode 100644 drivers/resctrl/mpam_devices.c
 create mode 100644 drivers/resctrl/mpam_internal.h

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index e51ccf1da102..ea3c54e04275 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig

@@ -2062,6 +2062,7 @@ config ARM64_TLB_RANGE
 
 config ARM64_MPAM
 	bool "Enable support for MPAM"
+	select ARM64_MPAM_DRIVER
 	select ACPI_MPAM if ACPI
 	help
 	  Memory Partitioning and Monitoring is an optional extension

diff --git a/drivers/Kconfig b/drivers/Kconfig
index 4915a63866b0..3054b50a2f4c 100644
--- a/drivers/Kconfig
+++ b/drivers/Kconfig

@@ -251,4 +251,6 @@ source "drivers/hte/Kconfig"
 
 source "drivers/cdx/Kconfig"
 
+source "drivers/resctrl/Kconfig"
+
 endmenu

diff --git a/drivers/Makefile b/drivers/Makefile
index b5749cf67044..f41cf4eddeba 100644
--- a/drivers/Makefile
+++ b/drivers/Makefile

@@ -194,5 +194,6 @@ obj-$(CONFIG_HTE)		+= hte/
 obj-$(CONFIG_DRM_ACCEL)		+= accel/
 obj-$(CONFIG_CDX_BUS)		+= cdx/
 obj-$(CONFIG_DPLL)		+= dpll/
+obj-y				+= resctrl/
 
 obj-$(CONFIG_S390)		+= s390/

diff --git a/drivers/resctrl/Kconfig b/drivers/resctrl/Kconfig
new file mode 100644
index 000000000000..dff7b87280ab
--- /dev/null
+++ b/drivers/resctrl/Kconfig

@@ -0,0 +1,11 @@
+# Confusingly, this is everything but the CPU bits of MPAM. CPU here means
+# CPU resources, not containers or cgroups etc.
+config ARM64_MPAM_DRIVER
+	bool "MPAM driver for System IP, e,g. caches and memory controllers"
+	depends on ARM64_MPAM && EXPERT
+
+config ARM64_MPAM_DRIVER_DEBUG
+	bool "Enable debug messages from the MPAM driver."
+	depends on ARM64_MPAM_DRIVER
+	help
+	  Say yes here to enable debug messages from the MPAM driver.

diff --git a/drivers/resctrl/Makefile b/drivers/resctrl/Makefile
new file mode 100644
index 000000000000..92b48fa20108
--- /dev/null
+++ b/drivers/resctrl/Makefile

@@ -0,0 +1,4 @@
+obj-$(CONFIG_ARM64_MPAM_DRIVER)			+= mpam.o
+mpam-y						+= mpam_devices.o
+
+cflags-$(CONFIG_ARM64_MPAM_DRIVER_DEBUG)	+= -DDEBUG

diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
new file mode 100644
index 000000000000..a0d9a699a6e7
--- /dev/null
+++ b/drivers/resctrl/mpam_devices.c

@@ -0,0 +1,336 @@
+// SPDX-License-Identifier: GPL-2.0
+// Copyright (C) 2025 Arm Ltd.
+
+#define pr_fmt(fmt) "%s:%s: " fmt, KBUILD_MODNAME, __func__
+
+#include <linux/acpi.h>
+#include <linux/arm_mpam.h>
+#include <linux/cacheinfo.h>
+#include <linux/cpu.h>
+#include <linux/cpumask.h>
+#include <linux/device.h>
+#include <linux/errno.h>
+#include <linux/gfp.h>
+#include <linux/list.h>
+#include <linux/lockdep.h>
+#include <linux/mutex.h>
+#include <linux/of.h>
+#include <linux/of_platform.h>
+#include <linux/platform_device.h>
+#include <linux/printk.h>
+#include <linux/slab.h>
+#include <linux/spinlock.h>
+#include <linux/srcu.h>
+#include <linux/types.h>
+
+#include <acpi/pcc.h>
+
+#include "mpam_internal.h"
+
+/*
+ * mpam_list_lock protects the SRCU lists when writing. Once the
+ * mpam_enabled key is enabled these lists are read-only,
+ * unless the error interrupt disables the driver.
+ */
+static DEFINE_MUTEX(mpam_list_lock);
+static LIST_HEAD(mpam_all_msc);
+
+static struct srcu_struct mpam_srcu;
+
+/* MPAM isn't available until all the MSC have been probed. */
+static u32 mpam_num_msc;
+
+static void mpam_discovery_complete(void)
+{
+	pr_err("Discovered all MSC\n");
+}
+
+static int mpam_dt_count_msc(void)
+{
+	int count = 0;
+	struct device_node *np;
+
+	for_each_compatible_node(np, NULL, "arm,mpam-msc") {
+		if (of_device_is_available(np))
+			count++;
+	}
+
+	return count;
+}
+
+static int mpam_dt_parse_resource(struct mpam_msc *msc, struct device_node *np,
+				  u32 ris_idx)
+{
+	int err = 0;
+	u32 level = 0;
+	unsigned long cache_id;
+	struct device_node *cache;
+
+	do {
+		if (of_device_is_compatible(np, "arm,mpam-cache")) {
+			cache = of_parse_phandle(np, "arm,mpam-device", 0);
+			if (!cache) {
+				pr_err("Failed to read phandle\n");
+				break;
+			}

+		}
+
+		list_add_rcu(&msc->glbl_list, &mpam_all_msc);
+		platform_set_drvdata(pdev, msc);
+	} while (0);
+	mutex_unlock(&mpam_list_lock);
+
+	if (!err) {
+		/* Create RIS entries described by firmware */
+		if (!acpi_disabled)
+			err = acpi_mpam_parse_resources(msc, plat_data);
+		else
+			err = mpam_dt_parse_resources(msc, plat_data);
+	}
+
+	if (!err && fw_num_msc == mpam_num_msc)
+		mpam_discovery_complete();
+
+	if (err && msc)
+		mpam_msc_drv_remove(pdev);
+
+	return err;
+}
+
+static const struct of_device_id mpam_of_match[] = {
+	{ .compatible = "arm,mpam-msc", },
+	{},
+};
+MODULE_DEVICE_TABLE(of, mpam_of_match);
+
+static struct platform_driver mpam_msc_driver = {
+	.driver = {
+		.name = "mpam_msc",
+		.of_match_table = of_match_ptr(mpam_of_match),
+	},
+	.probe = mpam_msc_drv_probe,
+	.remove = mpam_msc_drv_remove,
+};
+
+/*
+ * MSC that are hidden under caches are not created as platform devices
+ * as there is no cache driver. Caches are also special-cased in
+ * update_msc_accessibility().
+ */
+static void mpam_dt_create_foundling_msc(void)
+{
+	int err;
+	struct device_node *cache;
+
+	for_each_compatible_node(cache, NULL, "cache") {
+		err = of_platform_populate(cache, mpam_of_match, NULL, NULL);
+		if (err)
+			pr_err("Failed to create MSC devices under caches\n");
+	}
+}
+
+static int __init mpam_msc_driver_init(void)
+{
+	if (!system_supports_mpam())
+		return -EOPNOTSUPP;
+
+	init_srcu_struct(&mpam_srcu);
+
+	if (!acpi_disabled)
+		fw_num_msc = acpi_mpam_count_msc();
+	else
+		fw_num_msc = mpam_dt_count_msc();
+
+	if (fw_num_msc <= 0) {
+		pr_err("No MSC devices found in firmware\n");
+		return -EINVAL;
+	}
+
+	if (acpi_disabled)
+		mpam_dt_create_foundling_msc();
+
+	return platform_driver_register(&mpam_msc_driver);
+}
+subsys_initcall(mpam_msc_driver_init);

diff --git a/drivers/resctrl/mpam_internal.h b/drivers/resctrl/mpam_internal.h
new file mode 100644
index 000000000000..07e0f240eaca
--- /dev/null
+++ b/drivers/resctrl/mpam_internal.h

@@ -0,0 +1,62 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+// Copyright (C) 2024 Arm Ltd.
+
+#ifndef MPAM_INTERNAL_H
+#define MPAM_INTERNAL_H
+
+#include <linux/arm_mpam.h>
+#include <linux/cpumask.h>
+#include <linux/io.h>
+#include <linux/mailbox_client.h>
+#include <linux/mutex.h>
+#include <linux/resctrl.h>
+#include <linux/sizes.h>
+
+struct mpam_msc {
+	/* member of mpam_all_msc */
+	struct list_head        glbl_list;
+
+	int			id;
+	struct platform_device *pdev;
+
+	/* Not modified after mpam_is_enabled() becomes true */
+	enum mpam_msc_iface	iface;
+	u32			pcc_subspace_id;
+	struct mbox_client	pcc_cl;
+	struct pcc_mbox_chan	*pcc_chan;
+	u32			nrdy_usec;
+	cpumask_t		accessibility;
+
+	/*
+	 * probe_lock is only take during discovery. After discovery these