[PATCH v2 07/29] arm_mpam: Add probe/remove for mpam msc driver and kbuild boiler plate

James Morse
2025-09-10T20:44:05Z

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 <carl@os.amperecomputing.com>
Signed-off-by: James Morse <james.morse@arm.com>
---
Changes since v1:
* Avoid selecting driver on other architectrues.
* Removed PCC support stub.
* Use for_each_available_child_of_node_scoped() and of_property_read_reg()
* Clarified a comment.
* Stopped using mpam_num_msc as an id,a and made it atomic.
* Size of -1 returned from cache_of_calculate_id()
* Renamed some struct members.
* Made a bunch of pr_err() dev_err_ocne().
* Used more cleanup magic.
* Inlined a print message.
* Fixed error propagation from mpam_dt_parse_resources().
* Moved cache accessibility checks earlier.

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 | 14 +++
drivers/resctrl/Makefile | 4 +
drivers/resctrl/mpam_devices.c | 180 ++++++++++++++++++++++++++++++++
drivers/resctrl/mpam_internal.h | 65 ++++++++++++
7 files changed, 267 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 6487c511bdc6..93e563e1cce4 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 if EXPERT
select ACPI_MPAM if ACPI
help
Memory System Resource Partitioning and Monitoring (MPAM) is an
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-$(CONFIG_S390) += s390/
diff --git a/drivers/resctrl/Kconfig b/drivers/resctrl/Kconfig
new file mode 100644
index 000000000000..c30532a3a3a4
--- /dev/null
+++ b/drivers/resctrl/Kconfig
@@ -0,0 +1,14 @@
+menuconfig ARM64_MPAM_DRIVER
+ bool "MPAM driver"
+ depends on ARM64 && ARM64_MPAM && EXPERT
+ help
+ MPAM driver for System IP, e,g. caches and memory controllers.
+
+if ARM64_MPAM_DRIVER
+config ARM64_MPAM_DRIVER_DEBUG
+ bool "Enable debug messages from the MPAM driver"
+ depends on ARM64_MPAM_DRIVER
+ help
+ Say yes here to enable debug messages from the MPAM driver.
+
+endif
diff --git a/drivers/resctrl/Makefile b/drivers/resctrl/Makefile
new file mode 100644
index 000000000000..92b48fa20108
--- /dev/null
+++ b/drivers/resctrl/Makefile
@@ -0,0 +1,4 @@
+obj-$(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..efc4738e3b4d
--- /dev/null
+++ b/drivers/resctrl/mpam_devices.c
@@ -0,0 +1,180 @@
+// 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/platform_device.h>
+#include <linux/printk.h>
+#include <linux/slab.h>
+#include <linux/spinlock.h>
+#include <linux/srcu.h>
+#include <linux/types.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;
+
+/*
+ * Number of MSCs that have been probed. Once all MSC have been probed MPAM
+ * can be enabled.
+ */
+static atomic_t mpam_num_msc;
+
+/*
+ * An MSC can control traffic from a set of CPUs, but may only be accessible
+ * from a (hopefully wider) set of CPUs. The common reason for this is power
+ * management. If all the CPUs in a cluster are in PSCI:CPU_SUSPEND, the
+ * corresponding cache may also be powered off. By making accesses from
+ * one of those CPUs, we ensure this isn't the case.
+ */
+static int update_msc_accessibility(struct mpam_msc *msc)
+{
+ u32 affinity_id;
+ int err;
+
+ err = device_property_read_u32(&msc->pdev->dev, "cpu_affinity",
+ &affinity_id);
+ if (err)
+ cpumask_copy(&msc->accessibility, cpu_possible_mask);
+ else
+ acpi_pptt_get_cpus_from_container(affinity_id,
+ &msc->accessibility);
+
+ return 0;
+
+ return err;
+}
+
+static int fw_num_msc;
+
+static void mpam_msc_drv_remove(struct platform_device *pdev)
+{
+ struct mpam_msc *msc = platform_get_drvdata(pdev);
+
+ if (!msc)
+ return;
+
+ mutex_lock(&mpam_list_lock);
+ platform_set_drvdata(pdev, NULL);
+ list_del_rcu(&msc->all_msc_list);
+ synchronize_srcu(&mpam_srcu);
+ mutex_unlock(&mpam_list_lock);
+}
+
+static int mpam_msc_drv_probe(struct platform_device *pdev)
+{
+ int err;
+ struct mpam_msc *msc;
+ struct resource *msc_res;
+ struct device *dev = &pdev->dev;
+ void *plat_data = pdev->dev.platform_data;
+
+ mutex_lock(&mpam_list_lock);
+ do {
+ msc = devm_kzalloc(&pdev->dev, sizeof(*msc), GFP_KERNEL);
+ if (!msc) {
+ err = -ENOMEM;
+ break;
+ }
+
+ mutex_init(&msc->probe_lock);
+ mutex_init(&msc->part_sel_lock);
+ mutex_init(&msc->outer_mon_sel_lock);
+ raw_spin_lock_init(&msc->inner_mon_sel_lock);
+ msc->id = pdev->id;
+ msc->pdev = pdev;
+ INIT_LIST_HEAD_RCU(&msc->all_msc_list);
+ INIT_LIST_HEAD_RCU(&msc->ris);
+
+ err = update_msc_accessibility(msc);
+ if (err)
+ break;
+ if (cpumask_empty(&msc->accessibility)) {
+ dev_err_once(dev, "MSC is not accessible from any CPU!");
+ err = -EINVAL;
+ break;
+ }
+
+ if (device_property_read_u32(&pdev->dev, "pcc-channel",
+ &msc->pcc_subspace_id))
+ msc->iface = MPAM_IFACE_MMIO;
+ else
+ msc->iface = MPAM_IFACE_PCC;
+
+ if (msc->iface == MPAM_IFACE_MMIO) {
+ void __iomem *io;
+
+ io = devm_platform_get_and_ioremap_resource(pdev, 0,
+ &msc_res);
+ if (IS_ERR(io)) {
+ dev_err_once(dev, "Failed to map MSC base address\n");
+ err = PTR_ERR(io);
+ break;
+ }
+ msc->mapped_hwpage_sz = msc_res->end - msc_res->start;
+ msc->mapped_hwpage = io;
+ }
+
+ list_add_rcu(&msc->all_msc_list, &mpam_all_msc);
+ platform_set_drvdata(pdev, msc);
+ } while (0);
+ mutex_unlock(&mpam_list_lock);
+
+ if (!err) {
+ /* Create RIS entries described by firmware */
+ err = acpi_mpam_parse_resources(msc, plat_data);
+ }
+
+ if (err && msc)
+ mpam_msc_drv_remove(pdev);
+
+ if (!err && atomic_add_return(1, &mpam_num_msc) == fw_num_msc)
+ pr_info("Discovered all MSC\n");
+
+ return err;
+}
+
+static struct platform_driver mpam_msc_driver = {
+ .driver = {
+ .name = "mpam_msc",
+ },
+ .probe = mpam_msc_drv_probe,
+ .remove = mpam_msc_drv_remove,
+};
+
+static int __init mpam_msc_driver_init(void)
+{
+ if (!system_supports_mpam())
+ return -EOPNOTSUPP;
+
+ init_srcu_struct(&mpam_srcu);
+
+ fw_num_msc = acpi_mpam_count_msc();
+
+ if (fw_num_msc <= 0) {
+ pr_err("No MSC devices found in firmware\n");
+ return -EINVAL;
+ }
+
+ 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..7c63d590fc98
--- /dev/null
+++ b/drivers/resctrl/mpam_internal.h
@@ -0,0 +1,65 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+// Copyright (C) 2025 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 all_msc_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 taken during discovery. After discovery these
+ * properties become read-only and the lists are protected by SRCU.
+ */
+ struct mutex probe_lock;
+ unsigned long ris_idxs;
+ u32 ris_max;
+
+ /* mpam_msc_ris of this component */
+ struct list_head ris;
+
+ /*
+ * part_sel_lock protects access to the MSC hardware registers that are
+ * affected by MPAMCFG_PART_SEL. (including the ID registers that vary
+ * by RIS).
+ * If needed, take msc->probe_lock first.
+ */
+ struct mutex part_sel_lock;
+
+ /*
+ * mon_sel_lock protects access to the MSC hardware registers that are
+ * affected by MPAMCFG_MON_SEL.
+ * If needed, take msc->probe_lock first.
+ */
+ struct mutex outer_mon_sel_lock;
+ raw_spinlock_t inner_mon_sel_lock;
+ unsigned long inner_mon_sel_flags;
+
+ void __iomem *mapped_hwpage;
+ size_t mapped_hwpage_sz;
+};
+
+int mpam_get_cpumask_from_cache_id(unsigned long cache_id, u32 cache_level,
+ cpumask_t *affinity);
+
+#endif /* MPAM_INTERNAL_H */
--
2.39.5