[PATCH v5 08/10] arm_mpam: add MPAM-Fb MSC firmware access support

[Andre Przywara <andre.przywara@arm.com>]

The Arm MPAM Firmware-backed (Fb) Profile document[1] describes an
alternative way of accessing the "Memory System Components" (MSC) in an
MPAM enabled system.

Normally the MSCs are MMIO mapped, but in some implementations this
might not be possible (MSC located outside of the local socket, MSC
mapped secure-only) or desirable (direct MMIO access too slow or needs
to be mediated through a control processor). MPAM-fb standardises a
protocol to abstract MSC accesses, building on the SCMI protocol.

Add functions that do an MSC read or write access by redirecting the
request through a firmware interface. For now this done via an ACPI
PCC shared memory and mailbox combination.

Since the protocol used is only a small subset of the full SCMI spec,
and the SCMI protocol has no full ACPI support anyway, open-code the
(simple) SCMI message generation, for just the fields we need.

[1] https://developer.arm.com/documentation/den0144/latest

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
---
 drivers/resctrl/Makefile        |   2 +-
 drivers/resctrl/mpam_devices.c  |  52 ++++++--
 drivers/resctrl/mpam_fb.c       | 214 ++++++++++++++++++++++++++++++++
 drivers/resctrl/mpam_internal.h |  22 ++++
 include/linux/arm_mpam.h        |   2 +-
 5 files changed, 279 insertions(+), 13 deletions(-)
 create mode 100644 drivers/resctrl/mpam_fb.c

diff --git a/drivers/resctrl/Makefile b/drivers/resctrl/Makefile
index 4f6d0e81f9b8..097c036724e9 100644
--- a/drivers/resctrl/Makefile
+++ b/drivers/resctrl/Makefile
@@ -1,5 +1,5 @@
 obj-$(CONFIG_ARM64_MPAM_DRIVER)			+= mpam.o
-mpam-y						+= mpam_devices.o
+mpam-y						+= mpam_devices.o mpam_fb.o
 mpam-$(CONFIG_ARM64_MPAM_RESCTRL_FS)		+= mpam_resctrl.o
 
 ccflags-$(CONFIG_ARM64_MPAM_DRIVER_DEBUG)	+= -DDEBUG
diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
index f6910ab3bbc2..abe1e628928f 100644
--- a/drivers/resctrl/mpam_devices.c
+++ b/drivers/resctrl/mpam_devices.c
@@ -83,6 +83,16 @@ static DECLARE_WORK(mpam_broken_work, &mpam_disable);
 /* When mpam is disabled, the printed reason to aid debugging */
 static char *mpam_disable_reason;
 
+void mpam_fb_disable_mpam(int err)
+{
+	static char mpam_fb_reason[32];
+
+	snprintf(mpam_fb_reason, sizeof(mpam_fb_reason), "MPAM-Fb error %d",
+		 err);
+	mpam_disable_reason = mpam_fb_reason;
+	schedule_work(&mpam_broken_work);
+}
+
 /*
  * Whether resctrl has been setup. Used by cpuhp in preference to
  * mpam_is_enabled(). The disable call after an error interrupt makes
@@ -179,8 +189,11 @@ static void mpam_assert_partid_sizes_fixed(void)
 
 static int __mpam_read_reg(struct mpam_msc *msc, u16 reg, u32 *res)
 {
-	WARN_ON_ONCE(!cpumask_test_cpu(smp_processor_id(), &msc->accessibility));
 
+	if (msc->iface == MPAM_IFACE_PCC)
+		return mpam_fb_send_read_request(msc, reg, res);
+
+	WARN_ON_ONCE(!cpumask_test_cpu(smp_processor_id(), &msc->accessibility));
 	*res = readl_relaxed(msc->mapped_hwpage + reg);
 
 	return 0;
@@ -197,9 +210,12 @@ static inline int _mpam_read_partsel_reg(struct mpam_msc *msc, u16 reg,
 
 static int __mpam_write_reg(struct mpam_msc *msc, u16 reg, u32 val)
 {
-	WARN_ON_ONCE(reg + sizeof(u32) > msc->mapped_hwpage_sz);
-	WARN_ON_ONCE(!cpumask_test_cpu(smp_processor_id(), &msc->accessibility));
 
+	if (msc->iface == MPAM_IFACE_PCC)
+		return mpam_fb_send_write_request(msc, reg, val);
+
+	WARN_ON_ONCE(!cpumask_test_cpu(smp_processor_id(), &msc->accessibility));
+	WARN_ON_ONCE(reg + sizeof(u32) > msc->mapped_hwpage_sz);
 	writel_relaxed(val, msc->mapped_hwpage + reg);
 
 	return 0;
@@ -1141,8 +1157,11 @@ static int mpam_msc_read_mbwu_l(struct mpam_msc *msc, u64 *res)
 
 	mpam_mon_sel_lock_held(msc);
 
-	WARN_ON_ONCE((MSMON_MBWU_L + sizeof(u64)) > msc->mapped_hwpage_sz);
-	WARN_ON_ONCE(!cpumask_test_cpu(smp_processor_id(), &msc->accessibility));
+	if (msc->iface == MPAM_IFACE_MMIO) {
+		WARN_ON_ONCE((MSMON_MBWU_L + sizeof(u64)) > msc->mapped_hwpage_sz);
+		WARN_ON_ONCE(!cpumask_test_cpu(smp_processor_id(),
+			     &msc->accessibility));
+	}
 
 	ret = __mpam_read_reg(msc, MSMON_MBWU_L + 4, &mbwu_l_high2);
 	if (ret)
@@ -1176,8 +1195,11 @@ static int mpam_msc_zero_mbwu_l(struct mpam_msc *msc)
 
 	mpam_mon_sel_lock_held(msc);
 
-	WARN_ON_ONCE((MSMON_MBWU_L + sizeof(u64)) > msc->mapped_hwpage_sz);
-	WARN_ON_ONCE(!cpumask_test_cpu(smp_processor_id(), &msc->accessibility));
+	if (msc->iface == MPAM_IFACE_MMIO) {
+		WARN_ON_ONCE((MSMON_MBWU_L + sizeof(u64)) > msc->mapped_hwpage_sz);
+		WARN_ON_ONCE(!cpumask_test_cpu(smp_processor_id(),
+			     &msc->accessibility));
+	}
 
 	ret = __mpam_write_reg(msc, MSMON_MBWU_L, 0);
 	if (ret)
@@ -1490,11 +1512,16 @@ static int _msmon_read(struct mpam_component *comp, struct mon_read *arg)
 					 srcu_read_lock_held(&mpam_srcu)) {
 			arg->ris = ris;
 
-			err = smp_call_function_any(&msc->accessibility,
-						    __ris_msmon_read, arg,
-						    true);
-			if (!err && arg->err)
+			if (msc->iface == MPAM_IFACE_MMIO) {
+				err = smp_call_function_any(&msc->accessibility,
+							    __ris_msmon_read,
+							    arg, true);
+				if (!err)
+					err = arg->err;
+			} else {
+				__ris_msmon_read(arg);
 				err = arg->err;
+			}
 
 			/*
 			 * Save one error to be returned to the caller, but
@@ -1921,6 +1948,9 @@ static int mpam_get_msc_preferred_cpu(struct mpam_msc *msc)
 
 static int mpam_touch_msc(struct mpam_msc *msc, int (*fn)(void *a), void *arg)
 {
+	if (msc->iface != MPAM_IFACE_MMIO)
+		return fn(arg);
+
 	lockdep_assert_irqs_enabled();
 	lockdep_assert_cpus_held();
 	WARN_ON_ONCE(!srcu_read_lock_held((&mpam_srcu)));
diff --git a/drivers/resctrl/mpam_fb.c b/drivers/resctrl/mpam_fb.c
new file mode 100644
index 000000000000..dbe984241b0d
--- /dev/null
+++ b/drivers/resctrl/mpam_fb.c
@@ -0,0 +1,214 @@
+// SPDX-License-Identifier: GPL-2.0
+// Copyright (C) 2024-2026 Arm Ltd.
+
+#include <linux/arm_mpam.h>
+#include <linux/cleanup.h>
+#include <linux/errno.h>
+#include <linux/mailbox_client.h>
+#include <linux/mutex.h>
+#include <linux/types.h>
+
+#include <acpi/pcc.h>
+#include <asm/mpam.h>
+
+#include "mpam_internal.h"
+
+#define MPAM_FB_PROTOCOL_ID		0x1a
+
+#define MPAM_PROTOCOL_VERSION_CMD	0x0
+#define MPAM_MSC_ATTRIBUTES_CMD		0x3
+#define MPAM_MSC_READ_CMD		0x4
+#define MPAM_MSC_WRITE_CMD		0x5
+
+#define MPAM_FB_ERR_SUCCESS		 0
+#define MPAM_FB_ERR_NOT_SUPPORTED	-1
+#define MPAM_FB_ERR_INVALID_PARAMETERS	-2
+#define MPAM_FB_ERR_DENIED		-3
+#define MPAM_FB_ERR_NOT_FOUND		-4
+#define MPAM_FB_ERR_OUT_OF_RANGE	-5
+#define MPAM_FB_ERR_BUSY		-6
+#define MPAM_FB_ERR_COMMS_ERROR		-7
+#define MPAM_FB_ERR_GENERIC_ERROR	-8
+#define MPAM_FB_ERR_HW_ERROR		-9
+#define MPAM_FB_ERR_PROTOCOL_ERROR	-10
+#define MPAM_FB_ERR_IN_USE		-11
+
+#define MPAM_MSC_PROT_ID_MASK	GENMASK(17, 10)
+#define MPAM_MSC_TOKEN_MASK	GENMASK(27, 18)
+
+static atomic_t mpam_fb_token = ATOMIC_INIT(0);
+
+static void mpam_fb_build_version_message(unsigned int token,
+					  void __iomem *msg_buf)
+{
+	struct acpi_pcct_ext_pcc_shared_memory __iomem *pcc_shmem = msg_buf;
+
+	/* .signature is filled by the platform */
+	writel_relaxed(PCC_CMD_COMPLETION_NOTIFY, &pcc_shmem->flags);
+	writel_relaxed(MPAM_FB_PROT_HEADER_LEN, &pcc_shmem->length);
+	writel_relaxed(MPAM_PROTOCOL_VERSION_CMD |
+		       FIELD_PREP(MPAM_MSC_TOKEN_MASK, token) |
+		       FIELD_PREP(MPAM_MSC_PROT_ID_MASK, MPAM_FB_PROTOCOL_ID),
+		       &pcc_shmem->command);
+}
+
+static void mpam_fb_build_read_message(int msc_id, int reg, unsigned int token,
+				       void __iomem *msg_buf)
+{
+	struct acpi_pcct_ext_pcc_shared_memory __iomem *pcc_shmem = msg_buf;
+	struct mpam_fb_read_payload {
+		u32 msc_id;
+		u32 flags;
+		u32 reg_offset;
+	} __packed __iomem *payload = msg_buf + sizeof(*pcc_shmem);
+	int msg_size = MPAM_FB_PROT_HEADER_LEN + sizeof(*payload);
+
+	/* .signature is filled by the platform */
+	writel_relaxed(PCC_CMD_COMPLETION_NOTIFY, &pcc_shmem->flags);
+	writel_relaxed(msg_size, &pcc_shmem->length);
+	writel_relaxed(MPAM_MSC_READ_CMD |
+		       FIELD_PREP(MPAM_MSC_TOKEN_MASK, token) |
+		       FIELD_PREP(MPAM_MSC_PROT_ID_MASK, MPAM_FB_PROTOCOL_ID),
+		       &pcc_shmem->command);
+
+	writel_relaxed(msc_id, &payload->msc_id);
+	writel_relaxed(0, &payload->flags);
+	writel_relaxed(reg, &payload->reg_offset);
+}
+
+static void mpam_fb_build_write_message(int msc_id, int reg, u32 val,
+					unsigned int token,
+					void __iomem *msg_buf)
+{
+	struct acpi_pcct_ext_pcc_shared_memory __iomem *pcc_shmem = msg_buf;
+	struct mpam_fb_write_payload {
+		u32 msc_id;
+		u32 flags;
+		u32 reg_offset;
+		u32 value;
+	} __packed __iomem *payload = msg_buf + sizeof(*pcc_shmem);
+	int msg_size = MPAM_FB_PROT_HEADER_LEN + sizeof(*payload);
+
+	/* .signature is filled by the platform */
+	writel_relaxed(PCC_CMD_COMPLETION_NOTIFY, &pcc_shmem->flags);
+	writel_relaxed(msg_size, &pcc_shmem->length);
+	writel_relaxed(MPAM_MSC_WRITE_CMD |
+		       FIELD_PREP(MPAM_MSC_TOKEN_MASK, token) |
+		       FIELD_PREP(MPAM_MSC_PROT_ID_MASK, MPAM_FB_PROTOCOL_ID),
+		       &pcc_shmem->command);
+
+	writel_relaxed(msc_id, &payload->msc_id);
+	writel_relaxed(0, &payload->flags);
+	writel_relaxed(reg, &payload->reg_offset);
+	writel_relaxed(val, &payload->value);
+}
+
+static int mpam_fb_send_request(struct mpam_pcc_chan *pcc_chan, u32 msc_id,
+				u16 reg, u32 *result, int mpam_fb_command)
+{
+	unsigned int token = atomic_inc_return(&mpam_fb_token);
+	struct acpi_pcct_ext_pcc_shared_memory __iomem *pcc_shmem;
+	struct pcc_mbox_chan *chan;
+	void __iomem *payload_ofs;
+	u32 status;
+	int ret;
+
+	if (!pcc_chan)
+		return -ENODEV;
+
+	chan = pcc_chan->pcc_chan;
+
+	/* prune token to fit into the 10 bits inside the command register */
+	token = FIELD_GET(MPAM_MSC_TOKEN_MASK,
+			  FIELD_PREP(MPAM_MSC_TOKEN_MASK, token));
+
+	guard(mutex)(&pcc_chan->pcc_chan_lock);
+
+	switch (mpam_fb_command) {
+	case MPAM_MSC_WRITE_CMD:
+		mpam_fb_build_write_message(msc_id, reg, *result,
+					    token, chan->shmem);
+		break;
+	case MPAM_MSC_READ_CMD:
+		mpam_fb_build_read_message(msc_id, reg, token, chan->shmem);
+		break;
+	case MPAM_PROTOCOL_VERSION_CMD:
+		mpam_fb_build_version_message(token, chan->shmem);
+		break;
+	default:
+		dev_err(pcc_chan->pcc_cl.dev, "unsupported MPAM-Fb command %d\n",
+			mpam_fb_command);
+		ret = -EINVAL;
+		goto out_err;
+	}
+
+	ret = mbox_send_message(chan->mchan, NULL);
+	if (ret < 0)
+		goto out_err;
+
+	pcc_shmem = chan->shmem;
+	payload_ofs = chan->shmem + sizeof(*pcc_shmem);
+	status = readl(&pcc_shmem->command);
+	if (FIELD_GET(MPAM_MSC_TOKEN_MASK, status) != token) {
+		ret = -ETIMEDOUT;
+
+		goto out_err;
+	}
+
+	ret = readl(payload_ofs + 0x0);
+	if (ret < 0) {
+		switch (ret) {
+		case MPAM_FB_ERR_NOT_SUPPORTED:
+			ret = -EOPNOTSUPP;
+			break;
+		case MPAM_FB_ERR_INVALID_PARAMETERS:
+			ret = -EINVAL;
+			break;
+		case MPAM_FB_ERR_NOT_FOUND:
+			ret = -ENOENT;
+			break;
+		case MPAM_FB_ERR_OUT_OF_RANGE:
+			ret = -ERANGE;
+			break;
+		default:
+			ret = -EINVAL;
+		}
+
+		goto out_err;
+	}
+
+	if (mpam_fb_command != MPAM_MSC_WRITE_CMD)
+		*result = readl(payload_ofs + 0x4);
+
+	return 0;
+
+out_err:
+	mpam_fb_disable_mpam(ret);
+
+	return ret;
+}
+
+int mpam_fb_send_read_request(struct mpam_msc *msc, u16 reg, u32 *result)
+{
+	return mpam_fb_send_request(msc->pcc_chan, msc->mpam_fb_msc_id,
+				    reg, result, MPAM_MSC_READ_CMD);
+}
+
+int mpam_fb_send_write_request(struct mpam_msc *msc, u16 reg, u32 value)
+{
+	return mpam_fb_send_request(msc->pcc_chan, msc->mpam_fb_msc_id,
+				    reg, &value, MPAM_MSC_WRITE_CMD);
+}
+
+int mpam_fb_get_protocol_version(struct mpam_msc *msc)
+{
+	u32 version;
+	int ret;
+
+	ret = mpam_fb_send_request(msc->pcc_chan, 0,
+				   0, &version, MPAM_PROTOCOL_VERSION_CMD);
+	if (ret)
+		return ret;
+
+	return version;
+}
diff --git a/drivers/resctrl/mpam_internal.h b/drivers/resctrl/mpam_internal.h
index 2b81b6b0bf4e..a2193e7df57c 100644
--- a/drivers/resctrl/mpam_internal.h
+++ b/drivers/resctrl/mpam_internal.h
@@ -11,6 +11,7 @@
 #include <linux/io.h>
 #include <linux/jump_label.h>
 #include <linux/llist.h>
+#include <linux/mailbox_client.h>
 #include <linux/mutex.h>
 #include <linux/resctrl.h>
 #include <linux/spinlock.h>
@@ -57,6 +58,15 @@ struct mpam_garbage {
 	struct platform_device	*pdev;
 };
 
+struct mpam_pcc_chan {
+	struct list_head	pcc_chans;
+	struct mbox_client	pcc_cl;
+	struct pcc_mbox_chan	*pcc_chan;
+	struct mutex		pcc_chan_lock; /* only one message at a time */
+	struct kref		refcount;
+	int			subspace_id;
+};
+
 struct mpam_msc {
 	/* member of mpam_all_msc */
 	struct list_head	all_msc_list;
@@ -66,6 +76,8 @@ struct mpam_msc {
 
 	/* Not modified after mpam_is_enabled() becomes true */
 	enum mpam_msc_iface	iface;
+	struct mpam_pcc_chan	*pcc_chan;
+	int			mpam_fb_msc_id;	/* in its own name space */
 	u32			nrdy_usec;
 	cpumask_t		accessibility;
 	bool			has_extd_esr;
@@ -484,6 +496,9 @@ extern u8 mpam_pmg_max;
 void mpam_enable(struct work_struct *work);
 void mpam_disable(struct work_struct *work);
 
+/* helper function to call from outside mpam_devices.c */
+void mpam_fb_disable_mpam(int err);
+
 /* Reset all the RIS in a class under cpus_read_lock() */
 void mpam_reset_class_locked(struct mpam_class *class);
 
@@ -511,6 +526,13 @@ static inline void mpam_resctrl_offline_cpu(unsigned int cpu) { }
 static inline void mpam_resctrl_teardown_class(struct mpam_class *class) { }
 #endif /* CONFIG_RESCTRL_FS */
 
+/* MPAM-Fb Firmware-backed protocol wrappers */
+int mpam_fb_send_read_request(struct mpam_msc *msc, u16 reg, u32 *result);
+int mpam_fb_send_write_request(struct mpam_msc *msc, u16 reg, u32 value);
+int mpam_fb_get_protocol_version(struct mpam_msc *msc);
+
+#define MPAM_FB_PROT_HEADER_LEN		sizeof(u32)
+
 /*
  * MPAM MSCs have the following register layout. See:
  * Arm Memory System Resource Partitioning and Monitoring (MPAM) System
diff --git a/include/linux/arm_mpam.h b/include/linux/arm_mpam.h
index f92a36187a52..002f56e15362 100644
--- a/include/linux/arm_mpam.h
+++ b/include/linux/arm_mpam.h
@@ -12,7 +12,7 @@ struct mpam_msc;
 
 enum mpam_msc_iface {
 	MPAM_IFACE_MMIO,	/* a real MPAM MSC */
-	MPAM_IFACE_PCC,		/* a fake MPAM MSC */
+	MPAM_IFACE_PCC,		/* using the MPAM-Fb firmware redirection */
 };
 
 enum mpam_class_types {
-- 
2.43.0