[PATCH v4 00/10] arm_mpam: Add MPAM-Fb firmware support

[PATCH v4 00/10] arm_mpam: Add MPAM-Fb firmware support

[Andre Przywara]

Hi,

this is version 4 of the MPAM-Fb code, for firmware based MSC accesses.
Thanks to Jonathan's fearless review, a lot of the error handling has
been improved, mostly courtesy of new kernel toys like scoped_guard and
ACQUIRE(). Also the error handling pattern has been unified, to be
consistent within this series, but also to match common kernel patterns.
However I did not reorder the changes significantly, although some
patches have been squashed to avoid touching a line multiple times.
Also Ben, Niyas and Lee noticed bugs and other subtle issues, which have
been fixed. On top of that, the "nrdy" handling optimisation has been
dropped (for now).
Find a changelog below. Based on v7.2-rc1.

=======================
The Arm MPAM specification defines Memory System Components (MSCs),
which are devices that are programmed through an MMIO register frame. In
some occasions this turned out to be too limiting: the MSC might be
located behind a separate bus system (for instance inside an on-board
controller), it might be mapped secure-only, or in a different processor
socket without direct MMIO mapping. Also the MMIO access might be too slow
or it would need to be filtered or otherwise access controlled. Finally
there might be bugs in the MSC integration, which require a mediating
firmware to be accessible.

To accommodate all those different use cases, the MPAM-Fb specification
[1] describes an alternative way to access MSCs. Accesses to an MSC
would be wrapped in a message and communicated to the system using a
shared-memory/mailbox system mostly mimicking the Arm SCMI spec.
For ACPI systems, this would be abstracted through an ACPI PCC channel,
which provides the shared-memory region and the mailbox trigger. We can
lean on existing ACPI parsing code to register with these two
subsystems, but cannot rely on the existing SCMI code in the kernel.
This means we somewhat need to open code a very simplified SCMI handler,
which just provides enough functionality for the very basic subset of
SCMI that the MPAM-Fb spec requires.

The first six patches rework all MSC access wrappers to propagate error
information. Pure MMIO based MSC accesses would never fail, but the
MPAM-Fb access can go wrong in multiple ways. The patches have been split
up purely for reviewing reasons, if the number is a problem, we could as
well squash them.
Patch 7/10 solves a nasty problem: At the moment we protect stateful MSC
register accesses (mon_sel) through a spinlock. Unfortunately the mailbox
subsystem and the slow nature of the communication through this channel
forbid MPAM-Fb access in atomic context. So this patch keeps using a
spinlock for MMIO based accesses, but reverts to a mutex otherwise.
We just deny taking the lock for MPAM-Fb in atomic context, ideally we
wouldn't need that (no need to IPI another core when the MSC access does
not need to be local to one particular core), or we simply deny that part
of the functionality (access through perf).
Patch 8/10 adds the code to redirect MSC accesses through the
PCC shmem/mailbox system.
Patch 9/10 avoids the error IRQ handler to do an MSC access when using
MPAM_Fb, since those accesses cannot run in atomic context.
The final patch 10/10 then adds the code to detect and store the PCC
channel information from the ACPI tables, and eventually enables
MPAM-Fb accesses.

This would enable systems where some MSCs are not accessible via MMIO to
use those components anyway.

Please have a look and test!

Cheers,
Andre

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

Changes in v4:
- unify error check patterns
- use scoped_guard(mutex) and ACQUIRE to simplify error handling
- use struct kref for PCC channel refcount
- drop unused mailbox rx_callback function
- increase size of props[] array to hold new msc_id property
- set mailbox TX timeout based on ACPI MPAM table field
- use devm_mutex_init() to allow automatic cleanup
- avoid overwriting error value for arm,not-ready-us property read
- prune MPAM-Fb protocol token to fit into bitmask inside register
- check return value for AIDR read
- use two separate MPAM-Fb protocol payload structs
- prune header list for mpam_fb.c
- drop "nrdy handled as an error" change
- fix message size field in MPAM-Fb protocol shmem area
- drop message size return from MPAM-Fb message build functions
- bring back IRQ flag in MPAM-Fb protocol header

Changes in v3:
- drop inner/outer mon_sel lock patch, replace with simpler version
- harmonise code patterns in error propagation changes
- drop mon_sel lock before erroring out in mpam_ris_hw_probe_csu_nrdy()
- refactor mpam_msc_read_mbwu_l() to return an error
- drop special NRDY handling in __ris_msmon_read()
- add IRQ numbers in error interrupt handler to help pinpoint failure
- refactor MPAM-Fb message generation to accommodate more than read/write
- check MPAM-Fb protocol version at probe time
- drop mpam_fb.h header, merge into mpam_internal.h
- translate MPAM-Fb error code in Linux codes where needed
- clear IRQ flag bit in MPAM-Fb protocol header
- drop unneeded endianness conversions when crafting MPAM-Fb message
- use C struct to model MPAM-Fb message payload

Changes in v2:
- add patches to add error propagation to MSC access wrappers
- drop former patch 1/5 (not needed)
- drop lock in mpam_reprogram_msc(), to avoid double lock
- add support for multiple MSCs per PCC channel
- adjust SCMI protocol code to use a PCC subtype 3 channel
- let PCC code handle the PCC channel negotiation (due to subtype 3)
- drop SCMI names in shmem offsets, and use existing PCC type 3 struct
- adjust shmem field offsets to match MPAM-Fb spec, not pure SCMI
- prevent MPAM-Fb calls inside atomic smp_call_function_any() payload
- skip all MSC accesses inside the IRQ handler when using MPAM-Fb


Andre Przywara (10):
  arm_mpam: let low level MSC accessors return an error
  arm_mpam: propagate MSC access errors for hw_probe functions
  arm_mpam: propagate MSC access errors for MBWU counters
  arm_mpam: propagate MSC access errors for msmon helpers
  arm_mpam: propagate MSC access errors for __ris_msmon_read()
  arm_mpam: propagate MSC access errors for state saving function
  arm_mpam: prepare mon_sel locking for MPAM-Fb
  arm_mpam: add MPAM-Fb MSC firmware access support
  arm_mpam: prevent MPAM-Fb accesses inside IRQ handler
  arm_mpam: detect and enable MPAM-Fb PCC support

 drivers/acpi/arm64/mpam.c       |   6 +-
 drivers/resctrl/Makefile        |   2 +-
 drivers/resctrl/mpam_devices.c  | 648 ++++++++++++++++++++++++--------
 drivers/resctrl/mpam_fb.c       | 197 ++++++++++
 drivers/resctrl/mpam_internal.h |  60 ++-
 include/linux/arm_mpam.h        |   2 +-
 6 files changed, 739 insertions(+), 176 deletions(-)
 create mode 100644 drivers/resctrl/mpam_fb.c

-- 
2.43.0

[PATCH v4 01/10] arm_mpam: let low level MSC accessors return an error

[Andre Przywara]

The upcoming MPAM-Fb support does not use MMIO primitives to access an
MSC, but employs a shared-memory/doorbell based firmware protocol.
Its complexity means that is must be able to handle errors, whereas we
always assume an MMIO based MSC access succeeds today.

Change the __mpam_read_reg() low level accessor function to return the
requested data through a pointer, and return an error code instead.
Also change the __mpam_write_reg() accessor function to return an error
code. At the moment this is always 0, but this will change with alternative
MSC access methods.
Change all direct users of those MSC wrappers to comply with the new
prototypes, though the errors are not propagated all the way up yet.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
---
 drivers/resctrl/mpam_devices.c | 204 +++++++++++++++++++++------------
 1 file changed, 130 insertions(+), 74 deletions(-)

diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
index b69f99488111..912c21ce7f9f 100644
--- a/drivers/resctrl/mpam_devices.c
+++ b/drivers/resctrl/mpam_devices.c
@@ -177,59 +177,68 @@ static void mpam_assert_partid_sizes_fixed(void)
 		WARN_ON_ONCE(!partid_max_published);
 }
 
-static u32 __mpam_read_reg(struct mpam_msc *msc, u16 reg)
+static int __mpam_read_reg(struct mpam_msc *msc, u16 reg, u32 *res)
 {
 	WARN_ON_ONCE(!cpumask_test_cpu(smp_processor_id(), &msc->accessibility));
 
-	return readl_relaxed(msc->mapped_hwpage + reg);
+	*res = readl_relaxed(msc->mapped_hwpage + reg);
+
+	return 0;
 }
 
-static inline u32 _mpam_read_partsel_reg(struct mpam_msc *msc, u16 reg)
+static inline int _mpam_read_partsel_reg(struct mpam_msc *msc, u16 reg,
+					 u32 *res)
 {
 	lockdep_assert_held_once(&msc->part_sel_lock);
-	return __mpam_read_reg(msc, reg);
+	return __mpam_read_reg(msc, reg, res);
 }
 
-#define mpam_read_partsel_reg(msc, reg) _mpam_read_partsel_reg(msc, MPAMF_##reg)
+#define mpam_read_partsel_reg(msc, reg, res) _mpam_read_partsel_reg(msc, MPAMF_##reg, res)
 
-static void __mpam_write_reg(struct mpam_msc *msc, u16 reg, u32 val)
+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));
 
 	writel_relaxed(val, msc->mapped_hwpage + reg);
+
+	return 0;
 }
 
-static inline void _mpam_write_partsel_reg(struct mpam_msc *msc, u16 reg, u32 val)
+static inline int _mpam_write_partsel_reg(struct mpam_msc *msc, u16 reg, u32 val)
 {
 	lockdep_assert_held_once(&msc->part_sel_lock);
-	__mpam_write_reg(msc, reg, val);
+	return __mpam_write_reg(msc, reg, val);
 }
 
 #define mpam_write_partsel_reg(msc, reg, val)  _mpam_write_partsel_reg(msc, MPAMCFG_##reg, val)
 
-static inline u32 _mpam_read_monsel_reg(struct mpam_msc *msc, u16 reg)
+static inline int _mpam_read_monsel_reg(struct mpam_msc *msc, u16 reg,
+					u32 *res)
 {
 	mpam_mon_sel_lock_held(msc);
-	return __mpam_read_reg(msc, reg);
+	return __mpam_read_reg(msc, reg, res);
 }
 
-#define mpam_read_monsel_reg(msc, reg) _mpam_read_monsel_reg(msc, MSMON_##reg)
+#define mpam_read_monsel_reg(msc, reg, res) _mpam_read_monsel_reg(msc, MSMON_##reg, res)
 
-static inline void _mpam_write_monsel_reg(struct mpam_msc *msc, u16 reg, u32 val)
+static inline int _mpam_write_monsel_reg(struct mpam_msc *msc, u16 reg, u32 val)
 {
 	mpam_mon_sel_lock_held(msc);
-	__mpam_write_reg(msc, reg, val);
+	return __mpam_write_reg(msc, reg, val);
 }
 
 #define mpam_write_monsel_reg(msc, reg, val)   _mpam_write_monsel_reg(msc, MSMON_##reg, val)
 
 static bool mpam_msc_check_aidr(struct mpam_msc *msc)
 {
-	u32 aidr = __mpam_read_reg(msc, MPAMF_AIDR);
-	u32 major = FIELD_GET(MPAMF_AIDR_ARCH_MAJOR_REV, aidr);
-	u32 minor = FIELD_GET(MPAMF_AIDR_ARCH_MINOR_REV, aidr);
+	u32 aidr, major, minor;
 
+	if (__mpam_read_reg(msc, MPAMF_AIDR, &aidr))
+		return false;
+
+	major = FIELD_GET(MPAMF_AIDR_ARCH_MAJOR_REV, aidr);
+	minor = FIELD_GET(MPAMF_AIDR_ARCH_MINOR_REV, aidr);
 	/*
 	 * v0.0 and >v2.x aren't supported, but anything else should be backward
 	 * compatible to v0.1 or v1.0.
@@ -242,25 +251,39 @@ static bool mpam_msc_check_aidr(struct mpam_msc *msc)
 	return true;
 }
 
-static u64 mpam_msc_read_idr(struct mpam_msc *msc)
+static int mpam_msc_read_idr(struct mpam_msc *msc, u64 *res)
 {
-	u64 idr_high = 0, idr_low;
+	u32 idr_high = 0, idr_low;
+	int ret;
 
 	lockdep_assert_held(&msc->part_sel_lock);
 
-	idr_low = mpam_read_partsel_reg(msc, IDR);
-	if (FIELD_GET(MPAMF_IDR_EXT, idr_low))
-		idr_high = mpam_read_partsel_reg(msc, IDR + 4);
+	ret = mpam_read_partsel_reg(msc, IDR, &idr_low);
+	if (ret)
+		return ret;
+
+	if (FIELD_GET(MPAMF_IDR_EXT, idr_low)) {
+		ret = mpam_read_partsel_reg(msc, IDR + 4, &idr_high);
+		if (ret)
+			return ret;
+	}
 
-	return (idr_high << 32) | idr_low;
+	*res = ((u64)idr_high << 32) | idr_low;
+
+	return 0;
 }
 
-static void mpam_msc_clear_esr(struct mpam_msc *msc)
+static int mpam_msc_clear_esr(struct mpam_msc *msc)
 {
-	u64 esr_low = __mpam_read_reg(msc, MPAMF_ESR);
+	u32 esr_low;
+	int ret;
+
+	ret = __mpam_read_reg(msc, MPAMF_ESR, &esr_low);
+	if (ret)
+		return ret;
 
 	if (!esr_low)
-		return;
+		return 0;
 
 	/*
 	 * Clearing the high/low bits of MPAMF_ESR can not be atomic.
@@ -268,44 +291,57 @@ static void mpam_msc_clear_esr(struct mpam_msc *msc)
 	 * lower half prevent hardware from updating either half of the
 	 * register.
 	 */
-	if (msc->has_extd_esr)
-		__mpam_write_reg(msc, MPAMF_ESR + 4, 0);
-	__mpam_write_reg(msc, MPAMF_ESR, 0);
+	if (msc->has_extd_esr) {
+		ret = __mpam_write_reg(msc, MPAMF_ESR + 4, 0);
+		if (ret)
+			return ret;
+	}
+
+	return __mpam_write_reg(msc, MPAMF_ESR, 0);
 }
 
-static u64 mpam_msc_read_esr(struct mpam_msc *msc)
+static int mpam_msc_read_esr(struct mpam_msc *msc, u64 *res)
 {
-	u64 esr_high = 0, esr_low;
+	u32 esr_high = 0, esr_low;
+	int ret;
 
-	esr_low = __mpam_read_reg(msc, MPAMF_ESR);
-	if (msc->has_extd_esr)
-		esr_high = __mpam_read_reg(msc, MPAMF_ESR + 4);
+	ret = __mpam_read_reg(msc, MPAMF_ESR, &esr_low);
+	if (ret)
+		return ret;
 
-	return (esr_high << 32) | esr_low;
+	if (msc->has_extd_esr) {
+		ret = __mpam_read_reg(msc, MPAMF_ESR + 4, &esr_high);
+		if (ret)
+			return ret;
+	}
+
+	*res = ((u64)esr_high << 32) | esr_low;
+
+	return 0;
 }
 
-static void __mpam_part_sel_raw(u32 partsel, struct mpam_msc *msc)
+static int __mpam_part_sel_raw(u32 partsel, struct mpam_msc *msc)
 {
 	lockdep_assert_held(&msc->part_sel_lock);
 
-	mpam_write_partsel_reg(msc, PART_SEL, partsel);
+	return mpam_write_partsel_reg(msc, PART_SEL, partsel);
 }
 
-static void __mpam_part_sel(u8 ris_idx, u16 partid, struct mpam_msc *msc)
+static int __mpam_part_sel(u8 ris_idx, u16 partid, struct mpam_msc *msc)
 {
 	u32 partsel = FIELD_PREP(MPAMCFG_PART_SEL_RIS, ris_idx) |
 		      FIELD_PREP(MPAMCFG_PART_SEL_PARTID_SEL, partid);
 
-	__mpam_part_sel_raw(partsel, msc);
+	return __mpam_part_sel_raw(partsel, msc);
 }
 
-static void __mpam_intpart_sel(u8 ris_idx, u16 intpartid, struct mpam_msc *msc)
+static int __mpam_intpart_sel(u8 ris_idx, u16 intpartid, struct mpam_msc *msc)
 {
 	u32 partsel = FIELD_PREP(MPAMCFG_PART_SEL_RIS, ris_idx) |
 		      FIELD_PREP(MPAMCFG_PART_SEL_PARTID_SEL, intpartid) |
 		      MPAMCFG_PART_SEL_INTERNAL;
 
-	__mpam_part_sel_raw(partsel, msc);
+	return __mpam_part_sel_raw(partsel, msc);
 }
 
 int mpam_register_requestor(u16 partid_max, u8 pmg_max)
@@ -774,13 +810,13 @@ static bool mpam_ris_hw_probe_csu_nrdy(struct mpam_msc_ris *ris)
 	mpam_write_monsel_reg(msc, CFG_CSU_CTL, ctl_val);
 
 	_mpam_write_monsel_reg(msc, MSMON_CSU, MSMON___NRDY);
-	now = _mpam_read_monsel_reg(msc, MSMON_CSU);
+	_mpam_read_monsel_reg(msc, MSMON_CSU, &now);
 	can_set = now & MSMON___NRDY;
 
 	_mpam_write_monsel_reg(msc, MSMON_CSU, 0);
 	/* Configuration change to try and coax hardware into setting nrdy */
 	mpam_write_monsel_reg(msc, CFG_CSU_FLT, 0x1);
-	now = _mpam_read_monsel_reg(msc, MSMON_CSU);
+	_mpam_read_monsel_reg(msc, MSMON_CSU, &now);
 	can_clear = !(now & MSMON___NRDY);
 	mpam_mon_sel_unlock(msc);
 
@@ -800,7 +836,9 @@ static void mpam_ris_hw_probe(struct mpam_msc_ris *ris)
 
 	/* Cache Capacity Partitioning */
 	if (FIELD_GET(MPAMF_IDR_HAS_CCAP_PART, ris->idr)) {
-		u32 ccap_features = mpam_read_partsel_reg(msc, CCAP_IDR);
+		u32 ccap_features;
+
+		mpam_read_partsel_reg(msc, CCAP_IDR, &ccap_features);
 
 		props->cmax_wd = FIELD_GET(MPAMF_CCAP_IDR_CMAX_WD, ccap_features);
 		if (props->cmax_wd &&
@@ -823,7 +861,9 @@ static void mpam_ris_hw_probe(struct mpam_msc_ris *ris)
 
 	/* Cache Portion partitioning */
 	if (FIELD_GET(MPAMF_IDR_HAS_CPOR_PART, ris->idr)) {
-		u32 cpor_features = mpam_read_partsel_reg(msc, CPOR_IDR);
+		u32 cpor_features;
+
+		mpam_read_partsel_reg(msc, CPOR_IDR, &cpor_features);
 
 		props->cpbm_wd = FIELD_GET(MPAMF_CPOR_IDR_CPBM_WD, cpor_features);
 		if (props->cpbm_wd)
@@ -832,7 +872,9 @@ static void mpam_ris_hw_probe(struct mpam_msc_ris *ris)
 
 	/* Memory bandwidth partitioning */
 	if (FIELD_GET(MPAMF_IDR_HAS_MBW_PART, ris->idr)) {
-		u32 mbw_features = mpam_read_partsel_reg(msc, MBW_IDR);
+		u32 mbw_features;
+
+		mpam_read_partsel_reg(msc, MBW_IDR, &mbw_features);
 
 		/* portion bitmap resolution */
 		props->mbw_pbm_bits = FIELD_GET(MPAMF_MBW_IDR_BWPBM_WD, mbw_features);
@@ -860,7 +902,9 @@ static void mpam_ris_hw_probe(struct mpam_msc_ris *ris)
 
 	/* Priority partitioning */
 	if (FIELD_GET(MPAMF_IDR_HAS_PRI_PART, ris->idr)) {
-		u32 pri_features = mpam_read_partsel_reg(msc, PRI_IDR);
+		u32 pri_features;
+
+		mpam_read_partsel_reg(msc, PRI_IDR, &pri_features);
 
 		props->intpri_wd = FIELD_GET(MPAMF_PRI_IDR_INTPRI_WD, pri_features);
 		if (props->intpri_wd && FIELD_GET(MPAMF_PRI_IDR_HAS_INTPRI, pri_features)) {
@@ -879,7 +923,9 @@ static void mpam_ris_hw_probe(struct mpam_msc_ris *ris)
 
 	/* Performance Monitoring */
 	if (FIELD_GET(MPAMF_IDR_HAS_MSMON, ris->idr)) {
-		u32 msmon_features = mpam_read_partsel_reg(msc, MSMON_IDR);
+		u32 msmon_features;
+
+		mpam_read_partsel_reg(msc, MSMON_IDR, &msmon_features);
 
 		/*
 		 * If the firmware max-nrdy-us property is missing, the
@@ -892,7 +938,8 @@ static void mpam_ris_hw_probe(struct mpam_msc_ris *ris)
 		if (FIELD_GET(MPAMF_MSMON_IDR_MSMON_CSU, msmon_features)) {
 			u32 csumonidr;
 
-			csumonidr = mpam_read_partsel_reg(msc, CSUMON_IDR);
+			mpam_read_partsel_reg(msc, CSUMON_IDR, &csumonidr);
+
 			props->num_csu_mon = FIELD_GET(MPAMF_CSUMON_IDR_NUM_MON, csumonidr);
 			if (props->num_csu_mon) {
 				bool hw_managed;
@@ -915,7 +962,9 @@ static void mpam_ris_hw_probe(struct mpam_msc_ris *ris)
 		}
 		if (FIELD_GET(MPAMF_MSMON_IDR_MSMON_MBWU, msmon_features)) {
 			bool has_long;
-			u32 mbwumon_idr = mpam_read_partsel_reg(msc, MBWUMON_IDR);
+			u32 mbwumon_idr;
+
+			mpam_read_partsel_reg(msc, MBWUMON_IDR, &mbwumon_idr);
 
 			props->num_mbwu_mon = FIELD_GET(MPAMF_MBWUMON_IDR_NUM_MON, mbwumon_idr);
 			if (props->num_mbwu_mon) {
@@ -945,8 +994,11 @@ static void mpam_ris_hw_probe(struct mpam_msc_ris *ris)
 	 */
 	if (FIELD_GET(MPAMF_IDR_HAS_PARTID_NRW, ris->idr) &&
 	    class->type != MPAM_CLASS_UNKNOWN) {
-		u32 nrwidr = mpam_read_partsel_reg(msc, PARTID_NRW_IDR);
-		u16 partid_max = FIELD_GET(MPAMF_PARTID_NRW_IDR_INTPARTID_MAX, nrwidr);
+		u16 partid_max;
+		u32 nrwidr;
+
+		mpam_read_partsel_reg(msc, PARTID_NRW_IDR, &nrwidr);
+		partid_max = FIELD_GET(MPAMF_PARTID_NRW_IDR_INTPARTID_MAX, nrwidr);
 
 		mpam_set_feature(mpam_feat_partid_nrw, props);
 		msc->partid_max = min(msc->partid_max, partid_max);
@@ -970,8 +1022,9 @@ static int mpam_msc_hw_probe(struct mpam_msc *msc)
 
 	/* Grab an IDR value to find out how many RIS there are */
 	mutex_lock(&msc->part_sel_lock);
-	idr = mpam_msc_read_idr(msc);
-	msc->iidr = mpam_read_partsel_reg(msc, IIDR);
+	mpam_msc_read_idr(msc, &idr);
+	mpam_read_partsel_reg(msc, IIDR, &msc->iidr);
+
 	mutex_unlock(&msc->part_sel_lock);
 
 	mpam_enable_quirks(msc);
@@ -985,7 +1038,7 @@ static int mpam_msc_hw_probe(struct mpam_msc *msc)
 	for (ris_idx = 0; ris_idx <= msc->ris_max; ris_idx++) {
 		mutex_lock(&msc->part_sel_lock);
 		__mpam_part_sel(ris_idx, 0, msc);
-		idr = mpam_msc_read_idr(msc);
+		mpam_msc_read_idr(msc, &idr);
 		mutex_unlock(&msc->part_sel_lock);
 
 		partid_max = FIELD_GET(MPAMF_IDR_PARTID_MAX, idr);
@@ -1039,24 +1092,24 @@ static u64 mpam_msc_read_mbwu_l(struct mpam_msc *msc)
 {
 	int retry = 3;
 	u32 mbwu_l_low;
-	u64 mbwu_l_high1, mbwu_l_high2;
+	u32 mbwu_l_high1, mbwu_l_high2;
 
 	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));
 
-	mbwu_l_high2 = __mpam_read_reg(msc, MSMON_MBWU_L + 4);
+	__mpam_read_reg(msc, MSMON_MBWU_L + 4, &mbwu_l_high2);
 	do {
 		mbwu_l_high1 = mbwu_l_high2;
-		mbwu_l_low = __mpam_read_reg(msc, MSMON_MBWU_L);
-		mbwu_l_high2 = __mpam_read_reg(msc, MSMON_MBWU_L + 4);
+		__mpam_read_reg(msc, MSMON_MBWU_L, &mbwu_l_low);
+		__mpam_read_reg(msc, MSMON_MBWU_L + 4, &mbwu_l_high2);
 
 		retry--;
 	} while (mbwu_l_high1 != mbwu_l_high2 && retry > 0);
 
 	if (mbwu_l_high1 == mbwu_l_high2)
-		return (mbwu_l_high1 << 32) | mbwu_l_low;
+		return ((u64)mbwu_l_high1 << 32) | mbwu_l_low;
 
 	pr_warn("Failed to read a stable value\n");
 	return MSMON___L_NRDY;
@@ -1120,14 +1173,14 @@ static void read_msmon_ctl_flt_vals(struct mon_read *m, u32 *ctl_val,
 
 	switch (m->type) {
 	case mpam_feat_msmon_csu:
-		*ctl_val = mpam_read_monsel_reg(msc, CFG_CSU_CTL);
-		*flt_val = mpam_read_monsel_reg(msc, CFG_CSU_FLT);
+		mpam_read_monsel_reg(msc, CFG_CSU_CTL, ctl_val);
+		mpam_read_monsel_reg(msc, CFG_CSU_FLT, flt_val);
 		break;
 	case mpam_feat_msmon_mbwu_31counter:
 	case mpam_feat_msmon_mbwu_44counter:
 	case mpam_feat_msmon_mbwu_63counter:
-		*ctl_val = mpam_read_monsel_reg(msc, CFG_MBWU_CTL);
-		*flt_val = mpam_read_monsel_reg(msc, CFG_MBWU_FLT);
+		mpam_read_monsel_reg(msc, CFG_MBWU_CTL, ctl_val);
+		mpam_read_monsel_reg(msc, CFG_MBWU_FLT, flt_val);
 		break;
 	default:
 		pr_warn("Unexpected monitor type %d\n", m->type);
@@ -1206,6 +1259,7 @@ static u64 mpam_msmon_overflow_val(enum mpam_device_features type,
 static void __ris_msmon_read(void *arg)
 {
 	u64 now;
+	u32 now32;
 	bool nrdy = false;
 	bool config_mismatch;
 	bool overflow = false;
@@ -1268,9 +1322,9 @@ static void __ris_msmon_read(void *arg)
 
 	switch (m->type) {
 	case mpam_feat_msmon_csu:
-		now = mpam_read_monsel_reg(msc, CSU);
-		nrdy = now & MSMON___NRDY;
-		now = FIELD_GET(MSMON___VALUE, now);
+		mpam_read_monsel_reg(msc, CSU, &now32);
+		nrdy = now32 & MSMON___NRDY;
+		now = FIELD_GET(MSMON___VALUE, now32);
 
 		if (mpam_has_quirk(IGNORE_CSU_NRDY, msc) && m->waited_timeout)
 			nrdy = false;
@@ -1288,9 +1342,9 @@ static void __ris_msmon_read(void *arg)
 			else
 				now = FIELD_GET(MSMON___L_VALUE, now);
 		} else {
-			now = mpam_read_monsel_reg(msc, MBWU);
-			nrdy = now & MSMON___NRDY;
-			now = FIELD_GET(MSMON___VALUE, now);
+			mpam_read_monsel_reg(msc, MBWU, &now32);
+			nrdy = now32 & MSMON___NRDY;
+			now = FIELD_GET(MSMON___VALUE, now32);
 		}
 
 		if (mpam_has_quirk(T241_MBW_COUNTER_SCALE_64, msc) &&
@@ -1685,16 +1739,18 @@ static int mpam_save_mbwu_state(void *arg)
 		mon_sel = FIELD_PREP(MSMON_CFG_MON_SEL_MON_SEL, i) |
 			  FIELD_PREP(MSMON_CFG_MON_SEL_RIS, ris->ris_idx);
 		mpam_write_monsel_reg(msc, CFG_MON_SEL, mon_sel);
-
-		cur_flt = mpam_read_monsel_reg(msc, CFG_MBWU_FLT);
-		cur_ctl = mpam_read_monsel_reg(msc, CFG_MBWU_CTL);
+		mpam_read_monsel_reg(msc, CFG_MBWU_FLT, &cur_flt);
+		mpam_read_monsel_reg(msc, CFG_MBWU_CTL, &cur_ctl);
 		mpam_write_monsel_reg(msc, CFG_MBWU_CTL, 0);
 
 		if (mpam_ris_has_mbwu_long_counter(ris)) {
 			val = mpam_msc_read_mbwu_l(msc);
 			mpam_msc_zero_mbwu_l(msc);
 		} else {
-			val = mpam_read_monsel_reg(msc, MBWU);
+			u32 val32;
+
+			mpam_read_monsel_reg(msc, MBWU, &val32);
+			val = val32;
 			mpam_write_monsel_reg(msc, MBWU, 0);
 		}
 
@@ -2465,7 +2521,7 @@ static irqreturn_t __mpam_irq_handler(int irq, struct mpam_msc *msc)
 					   &msc->accessibility)))
 		return IRQ_NONE;
 
-	reg = mpam_msc_read_esr(msc);
+	mpam_msc_read_esr(msc, &reg);
 
 	errcode = FIELD_GET(MPAMF_ESR_ERRCODE, reg);
 	if (!errcode)
-- 
2.43.0

[PATCH v4 02/10] arm_mpam: propagate MSC access errors for hw_probe functions

[Andre Przywara]

Allow the functions probing for MSC hardware and features to return an
error, and propagate read and write errors from the lower level up.
This uses some "scoped cleanup" functions like scoped_guard() and
ACQUIRE() to avoid the complexity of error handling when a lock has been
taken. Since the mon_sel_lock is a bit special (even more so in an
upcoming patch), we define a new GUARD type for it.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
---
 drivers/resctrl/mpam_devices.c  | 127 +++++++++++++++++++++-----------
 drivers/resctrl/mpam_internal.h |   8 ++
 2 files changed, 91 insertions(+), 44 deletions(-)

diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
index 912c21ce7f9f..ecd45a585942 100644
--- a/drivers/resctrl/mpam_devices.c
+++ b/drivers/resctrl/mpam_devices.c
@@ -794,38 +794,46 @@ static bool mpam_ris_hw_probe_csu_nrdy(struct mpam_msc_ris *ris)
 	bool can_set, can_clear;
 	struct mpam_msc *msc = ris->vmsc->msc;
 
-	if (WARN_ON_ONCE(!mpam_mon_sel_lock(msc)))
+	ACQUIRE(mon_sel_lock, guard)(msc);
+	if (ACQUIRE_ERR(mon_sel_lock, &guard))
 		return false;
 
 	mon_sel = FIELD_PREP(MSMON_CFG_MON_SEL_MON_SEL, 0) |
 		  FIELD_PREP(MSMON_CFG_MON_SEL_RIS, ris->ris_idx);
-	mpam_write_monsel_reg(msc, CFG_MON_SEL, mon_sel);
+	if (mpam_write_monsel_reg(msc, CFG_MON_SEL, mon_sel))
+		return false;
 
 	/* Hardware might ignore nrdy if it's not enabled */
 	ctl_val = MSMON_CFG_CSU_CTL_TYPE_CSU;
 	ctl_val |= MSMON_CFG_x_CTL_MATCH_PARTID;
 	ctl_val |= MSMON_CFG_x_CTL_MATCH_PMG;
 	ctl_val |= MSMON_CFG_x_CTL_EN;
-	mpam_write_monsel_reg(msc, CFG_CSU_FLT, 0);
-	mpam_write_monsel_reg(msc, CFG_CSU_CTL, ctl_val);
+	if (mpam_write_monsel_reg(msc, CFG_CSU_FLT, 0))
+		return false;
+	if (mpam_write_monsel_reg(msc, CFG_CSU_CTL, ctl_val))
+		return false;
 
-	_mpam_write_monsel_reg(msc, MSMON_CSU, MSMON___NRDY);
-	_mpam_read_monsel_reg(msc, MSMON_CSU, &now);
+	if (_mpam_write_monsel_reg(msc, MSMON_CSU, MSMON___NRDY))
+		return false;
+	if (_mpam_read_monsel_reg(msc, MSMON_CSU, &now))
+		return false;
 	can_set = now & MSMON___NRDY;
 
-	_mpam_write_monsel_reg(msc, MSMON_CSU, 0);
+	if (_mpam_write_monsel_reg(msc, MSMON_CSU, 0))
+		return false;
 	/* Configuration change to try and coax hardware into setting nrdy */
-	mpam_write_monsel_reg(msc, CFG_CSU_FLT, 0x1);
-	_mpam_read_monsel_reg(msc, MSMON_CSU, &now);
+	if (mpam_write_monsel_reg(msc, CFG_CSU_FLT, 0x1))
+		return false;
+	if (_mpam_read_monsel_reg(msc, MSMON_CSU, &now))
+		return false;
 	can_clear = !(now & MSMON___NRDY);
-	mpam_mon_sel_unlock(msc);
 
 	return (!can_set || !can_clear);
 }
 
-static void mpam_ris_hw_probe(struct mpam_msc_ris *ris)
+static int mpam_ris_hw_probe(struct mpam_msc_ris *ris)
 {
-	int err;
+	int fw_has_nrdy_err, err;
 	struct mpam_msc *msc = ris->vmsc->msc;
 	struct device *dev = &msc->pdev->dev;
 	struct mpam_props *props = &ris->props;
@@ -838,7 +846,9 @@ static void mpam_ris_hw_probe(struct mpam_msc_ris *ris)
 	if (FIELD_GET(MPAMF_IDR_HAS_CCAP_PART, ris->idr)) {
 		u32 ccap_features;
 
-		mpam_read_partsel_reg(msc, CCAP_IDR, &ccap_features);
+		err = mpam_read_partsel_reg(msc, CCAP_IDR, &ccap_features);
+		if (err)
+			return err;
 
 		props->cmax_wd = FIELD_GET(MPAMF_CCAP_IDR_CMAX_WD, ccap_features);
 		if (props->cmax_wd &&
@@ -863,7 +873,9 @@ static void mpam_ris_hw_probe(struct mpam_msc_ris *ris)
 	if (FIELD_GET(MPAMF_IDR_HAS_CPOR_PART, ris->idr)) {
 		u32 cpor_features;
 
-		mpam_read_partsel_reg(msc, CPOR_IDR, &cpor_features);
+		err = mpam_read_partsel_reg(msc, CPOR_IDR, &cpor_features);
+		if (err)
+			return err;
 
 		props->cpbm_wd = FIELD_GET(MPAMF_CPOR_IDR_CPBM_WD, cpor_features);
 		if (props->cpbm_wd)
@@ -873,8 +885,9 @@ static void mpam_ris_hw_probe(struct mpam_msc_ris *ris)
 	/* Memory bandwidth partitioning */
 	if (FIELD_GET(MPAMF_IDR_HAS_MBW_PART, ris->idr)) {
 		u32 mbw_features;
-
-		mpam_read_partsel_reg(msc, MBW_IDR, &mbw_features);
+		err = mpam_read_partsel_reg(msc, MBW_IDR, &mbw_features);
+		if (err)
+			return err;
 
 		/* portion bitmap resolution */
 		props->mbw_pbm_bits = FIELD_GET(MPAMF_MBW_IDR_BWPBM_WD, mbw_features);
@@ -903,8 +916,9 @@ static void mpam_ris_hw_probe(struct mpam_msc_ris *ris)
 	/* Priority partitioning */
 	if (FIELD_GET(MPAMF_IDR_HAS_PRI_PART, ris->idr)) {
 		u32 pri_features;
-
-		mpam_read_partsel_reg(msc, PRI_IDR, &pri_features);
+		err = mpam_read_partsel_reg(msc, PRI_IDR, &pri_features);
+		if (err)
+			return err;
 
 		props->intpri_wd = FIELD_GET(MPAMF_PRI_IDR_INTPRI_WD, pri_features);
 		if (props->intpri_wd && FIELD_GET(MPAMF_PRI_IDR_HAS_INTPRI, pri_features)) {
@@ -925,20 +939,24 @@ static void mpam_ris_hw_probe(struct mpam_msc_ris *ris)
 	if (FIELD_GET(MPAMF_IDR_HAS_MSMON, ris->idr)) {
 		u32 msmon_features;
 
-		mpam_read_partsel_reg(msc, MSMON_IDR, &msmon_features);
+		err = mpam_read_partsel_reg(msc, MSMON_IDR, &msmon_features);
+		if (err)
+			return err;
 
 		/*
 		 * If the firmware max-nrdy-us property is missing, the
 		 * CSU counters can't be used. Should we wait forever?
 		 */
-		err = device_property_read_u32(&msc->pdev->dev,
-					       "arm,not-ready-us",
-					       &msc->nrdy_usec);
+		fw_has_nrdy_err = device_property_read_u32(&msc->pdev->dev,
+							   "arm,not-ready-us",
+							   &msc->nrdy_usec);
 
 		if (FIELD_GET(MPAMF_MSMON_IDR_MSMON_CSU, msmon_features)) {
 			u32 csumonidr;
 
-			mpam_read_partsel_reg(msc, CSUMON_IDR, &csumonidr);
+			err = mpam_read_partsel_reg(msc, CSUMON_IDR, &csumonidr);
+			if (err)
+				return err;
 
 			props->num_csu_mon = FIELD_GET(MPAMF_CSUMON_IDR_NUM_MON, csumonidr);
 			if (props->num_csu_mon) {
@@ -956,7 +974,7 @@ static void mpam_ris_hw_probe(struct mpam_msc_ris *ris)
 				 * Accept the missing firmware property if NRDY appears
 				 * un-implemented.
 				 */
-				if (err && hw_managed)
+				if (fw_has_nrdy_err && hw_managed)
 					dev_err_once(dev, "Counters are not usable because not-ready timeout was not provided by firmware.");
 			}
 		}
@@ -964,7 +982,9 @@ static void mpam_ris_hw_probe(struct mpam_msc_ris *ris)
 			bool has_long;
 			u32 mbwumon_idr;
 
-			mpam_read_partsel_reg(msc, MBWUMON_IDR, &mbwumon_idr);
+			err = mpam_read_partsel_reg(msc, MBWUMON_IDR, &mbwumon_idr);
+			if (err)
+				return err;
 
 			props->num_mbwu_mon = FIELD_GET(MPAMF_MBWUMON_IDR_NUM_MON, mbwumon_idr);
 			if (props->num_mbwu_mon) {
@@ -997,16 +1017,22 @@ static void mpam_ris_hw_probe(struct mpam_msc_ris *ris)
 		u16 partid_max;
 		u32 nrwidr;
 
-		mpam_read_partsel_reg(msc, PARTID_NRW_IDR, &nrwidr);
+		err = mpam_read_partsel_reg(msc, PARTID_NRW_IDR, &nrwidr);
+		if (err)
+			return err;
+
 		partid_max = FIELD_GET(MPAMF_PARTID_NRW_IDR_INTPARTID_MAX, nrwidr);
 
 		mpam_set_feature(mpam_feat_partid_nrw, props);
 		msc->partid_max = min(msc->partid_max, partid_max);
 	}
+
+	return 0;
 }
 
 static int mpam_msc_hw_probe(struct mpam_msc *msc)
 {
+	int ret;
 	u64 idr;
 	u16 partid_max;
 	u8 ris_idx, pmg_max;
@@ -1021,11 +1047,14 @@ static int mpam_msc_hw_probe(struct mpam_msc *msc)
 	}
 
 	/* Grab an IDR value to find out how many RIS there are */
-	mutex_lock(&msc->part_sel_lock);
-	mpam_msc_read_idr(msc, &idr);
-	mpam_read_partsel_reg(msc, IIDR, &msc->iidr);
-
-	mutex_unlock(&msc->part_sel_lock);
+	scoped_guard(mutex, &msc->part_sel_lock) {
+		ret = mpam_msc_read_idr(msc, &idr);
+		if (ret)
+			return ret;
+		ret = mpam_read_partsel_reg(msc, IIDR, &msc->iidr);
+		if (ret)
+			return ret;
+	}
 
 	mpam_enable_quirks(msc);
 
@@ -1036,10 +1065,15 @@ static int mpam_msc_hw_probe(struct mpam_msc *msc)
 	msc->pmg_max = FIELD_GET(MPAMF_IDR_PMG_MAX, idr);
 
 	for (ris_idx = 0; ris_idx <= msc->ris_max; ris_idx++) {
-		mutex_lock(&msc->part_sel_lock);
-		__mpam_part_sel(ris_idx, 0, msc);
-		mpam_msc_read_idr(msc, &idr);
-		mutex_unlock(&msc->part_sel_lock);
+		scoped_guard(mutex, &msc->part_sel_lock) {
+			ret = __mpam_part_sel(ris_idx, 0, msc);
+			if (ret)
+				return ret;
+
+			ret = mpam_msc_read_idr(msc, &idr);
+			if (ret)
+				return ret;
+		}
 
 		partid_max = FIELD_GET(MPAMF_IDR_PARTID_MAX, idr);
 		pmg_max = FIELD_GET(MPAMF_IDR_PMG_MAX, idr);
@@ -1047,17 +1081,22 @@ static int mpam_msc_hw_probe(struct mpam_msc *msc)
 		msc->pmg_max = min(msc->pmg_max, pmg_max);
 		msc->has_extd_esr = FIELD_GET(MPAMF_IDR_HAS_EXTD_ESR, idr);
 
-		mutex_lock(&mpam_list_lock);
-		ris = mpam_get_or_create_ris(msc, ris_idx);
-		mutex_unlock(&mpam_list_lock);
-		if (IS_ERR(ris))
-			return PTR_ERR(ris);
+		scoped_guard(mutex, &mpam_list_lock) {
+			ris = mpam_get_or_create_ris(msc, ris_idx);
+			if (IS_ERR(ris))
+				return PTR_ERR(ris);
+		}
 		ris->idr = idr;
 
-		mutex_lock(&msc->part_sel_lock);
-		__mpam_part_sel(ris_idx, 0, msc);
-		mpam_ris_hw_probe(ris);
-		mutex_unlock(&msc->part_sel_lock);
+		scoped_guard(mutex, &msc->part_sel_lock) {
+			ret = __mpam_part_sel(ris_idx, 0, msc);
+			if (ret)
+				return ret;
+
+			ret = mpam_ris_hw_probe(ris);
+			if (ret)
+				return ret;
+		}
 	}
 
 	/* Clear any stale errors */
diff --git a/drivers/resctrl/mpam_internal.h b/drivers/resctrl/mpam_internal.h
index 04d1a59f02af..0c3f6a040b20 100644
--- a/drivers/resctrl/mpam_internal.h
+++ b/drivers/resctrl/mpam_internal.h
@@ -162,6 +162,14 @@ static inline void mpam_mon_sel_lock_init(struct mpam_msc *msc)
 	raw_spin_lock_init(&msc->_mon_sel_lock);
 }
 
+DEFINE_GUARD(mon_sel,
+	     struct mpam_msc *,
+	     mpam_mon_sel_lock(_T),
+	     mpam_mon_sel_unlock(_T));
+DEFINE_GUARD_COND(mon_sel, _lock,
+		  mpam_mon_sel_lock(_T),
+		  _RET);
+
 /* Bits for mpam features bitmaps */
 enum mpam_device_features {
 	mpam_feat_cpor_part,
-- 
2.43.0

[PATCH v4 03/10] arm_mpam: propagate MSC access errors for MBWU counters

[Andre Przywara]

Allow the mpam_msc_read_mbwu_l() function to return an error, and
propagate errors from the lower level up. This also changes the users
of this function.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
---
 drivers/resctrl/mpam_devices.c | 45 +++++++++++++++++++++++-----------
 1 file changed, 31 insertions(+), 14 deletions(-)

diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
index ecd45a585942..fce29fa9ef78 100644
--- a/drivers/resctrl/mpam_devices.c
+++ b/drivers/resctrl/mpam_devices.c
@@ -1127,8 +1127,9 @@ static bool mpam_ris_has_mbwu_long_counter(struct mpam_msc_ris *ris)
 		mpam_has_feature(mpam_feat_msmon_mbwu_44counter, &ris->props));
 }
 
-static u64 mpam_msc_read_mbwu_l(struct mpam_msc *msc)
+static int mpam_msc_read_mbwu_l(struct mpam_msc *msc, u64 *res)
 {
+	int ret;
 	int retry = 3;
 	u32 mbwu_l_low;
 	u32 mbwu_l_high1, mbwu_l_high2;
@@ -1138,20 +1139,30 @@ static u64 mpam_msc_read_mbwu_l(struct mpam_msc *msc)
 	WARN_ON_ONCE((MSMON_MBWU_L + sizeof(u64)) > msc->mapped_hwpage_sz);
 	WARN_ON_ONCE(!cpumask_test_cpu(smp_processor_id(), &msc->accessibility));
 
-	__mpam_read_reg(msc, MSMON_MBWU_L + 4, &mbwu_l_high2);
+	ret = __mpam_read_reg(msc, MSMON_MBWU_L + 4, &mbwu_l_high2);
+	if (ret)
+		return ret;
+
 	do {
 		mbwu_l_high1 = mbwu_l_high2;
-		__mpam_read_reg(msc, MSMON_MBWU_L, &mbwu_l_low);
-		__mpam_read_reg(msc, MSMON_MBWU_L + 4, &mbwu_l_high2);
+		ret = __mpam_read_reg(msc, MSMON_MBWU_L, &mbwu_l_low);
+		if (ret)
+			return ret;
+		ret = __mpam_read_reg(msc, MSMON_MBWU_L + 4, &mbwu_l_high2);
+		if (ret)
+			return ret;
 
 		retry--;
 	} while (mbwu_l_high1 != mbwu_l_high2 && retry > 0);
 
-	if (mbwu_l_high1 == mbwu_l_high2)
-		return ((u64)mbwu_l_high1 << 32) | mbwu_l_low;
+	if (mbwu_l_high1 == mbwu_l_high2) {
+		*res = ((u64)mbwu_l_high1 << 32) | mbwu_l_low;
+	} else {
+		pr_warn("Failed to read a stable value\n");
+		*res = MSMON___L_NRDY;
+	}
 
-	pr_warn("Failed to read a stable value\n");
-	return MSMON___L_NRDY;
+	return 0;
 }
 
 static void mpam_msc_zero_mbwu_l(struct mpam_msc *msc)
@@ -1310,10 +1321,12 @@ static void __ris_msmon_read(void *arg)
 	struct mpam_msc *msc = m->ris->vmsc->msc;
 	u32 mon_sel, ctl_val, flt_val, cur_ctl, cur_flt;
 
-	if (!mpam_mon_sel_lock(msc)) {
+	ACQUIRE(mon_sel_lock, guard)(msc);
+	if (ACQUIRE_ERR(mon_sel_lock, &guard)) {
 		m->err = -EIO;
 		return;
 	}
+
 	mon_sel = FIELD_PREP(MSMON_CFG_MON_SEL_MON_SEL, ctx->mon) |
 		  FIELD_PREP(MSMON_CFG_MON_SEL_RIS, ris->ris_idx);
 	mpam_write_monsel_reg(msc, CFG_MON_SEL, mon_sel);
@@ -1373,7 +1386,9 @@ static void __ris_msmon_read(void *arg)
 	case mpam_feat_msmon_mbwu_44counter:
 	case mpam_feat_msmon_mbwu_63counter:
 		if (m->type != mpam_feat_msmon_mbwu_31counter) {
-			now = mpam_msc_read_mbwu_l(msc);
+			m->err = mpam_msc_read_mbwu_l(msc, &now);
+			if (m->err)
+				return;
 			nrdy = now & MSMON___L_NRDY;
 
 			if (m->type == mpam_feat_msmon_mbwu_63counter)
@@ -1407,7 +1422,6 @@ static void __ris_msmon_read(void *arg)
 	default:
 		m->err = -EINVAL;
 	}
-	mpam_mon_sel_unlock(msc);
 
 	if (nrdy)
 		m->err = -EBUSY;
@@ -1762,6 +1776,7 @@ static int mpam_save_mbwu_state(void *arg)
 {
 	int i;
 	u64 val;
+	int ret;
 	struct mon_cfg *cfg;
 	u32 cur_flt, cur_ctl, mon_sel;
 	struct mpam_msc_ris *ris = arg;
@@ -1772,7 +1787,8 @@ static int mpam_save_mbwu_state(void *arg)
 		mbwu_state = &ris->mbwu_state[i];
 		cfg = &mbwu_state->cfg;
 
-		if (WARN_ON_ONCE(!mpam_mon_sel_lock(msc)))
+		ACQUIRE(mon_sel_lock, guard)(msc);
+		if (ACQUIRE_ERR(mon_sel_lock, &guard))
 			return -EIO;
 
 		mon_sel = FIELD_PREP(MSMON_CFG_MON_SEL_MON_SEL, i) |
@@ -1783,7 +1799,9 @@ static int mpam_save_mbwu_state(void *arg)
 		mpam_write_monsel_reg(msc, CFG_MBWU_CTL, 0);
 
 		if (mpam_ris_has_mbwu_long_counter(ris)) {
-			val = mpam_msc_read_mbwu_l(msc);
+			ret = mpam_msc_read_mbwu_l(msc, &val);
+			if (ret)
+				return ret;
 			mpam_msc_zero_mbwu_l(msc);
 		} else {
 			u32 val32;
@@ -1799,7 +1817,6 @@ static int mpam_save_mbwu_state(void *arg)
 		cfg->partid = FIELD_GET(MSMON_CFG_x_FLT_PARTID, cur_flt);
 		mbwu_state->correction += val;
 		mbwu_state->enabled = FIELD_GET(MSMON_CFG_x_CTL_EN, cur_ctl);
-		mpam_mon_sel_unlock(msc);
 	}
 
 	return 0;
-- 
2.43.0

[PATCH v4 04/10] arm_mpam: propagate MSC access errors for msmon helpers

[Andre Przywara]

Allow the helper functions for msmon accesses to return an error, and
propagate read and write errors from the lower level up.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
---
 drivers/resctrl/mpam_devices.c | 72 ++++++++++++++++++++++------------
 1 file changed, 47 insertions(+), 25 deletions(-)

diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
index fce29fa9ef78..9ee4eb4db03f 100644
--- a/drivers/resctrl/mpam_devices.c
+++ b/drivers/resctrl/mpam_devices.c
@@ -1165,15 +1165,20 @@ static int mpam_msc_read_mbwu_l(struct mpam_msc *msc, u64 *res)
 	return 0;
 }
 
-static void mpam_msc_zero_mbwu_l(struct mpam_msc *msc)
+static int mpam_msc_zero_mbwu_l(struct mpam_msc *msc)
 {
+	int ret;
+
 	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));
 
-	__mpam_write_reg(msc, MSMON_MBWU_L, 0);
-	__mpam_write_reg(msc, MSMON_MBWU_L + 4, 0);
+	ret = __mpam_write_reg(msc, MSMON_MBWU_L, 0);
+	if (ret)
+		return ret;
+
+	return __mpam_write_reg(msc, MSMON_MBWU_L + 4, 0);
 }
 
 static void gen_msmon_ctl_flt_vals(struct mon_read *m, u32 *ctl_val,
@@ -1216,24 +1221,28 @@ static void gen_msmon_ctl_flt_vals(struct mon_read *m, u32 *ctl_val,
 	}
 }
 
-static void read_msmon_ctl_flt_vals(struct mon_read *m, u32 *ctl_val,
-				    u32 *flt_val)
+static int read_msmon_ctl_flt_vals(struct mon_read *m, u32 *ctl_val,
+				   u32 *flt_val)
 {
 	struct mpam_msc *msc = m->ris->vmsc->msc;
+	int ret;
 
 	switch (m->type) {
 	case mpam_feat_msmon_csu:
-		mpam_read_monsel_reg(msc, CFG_CSU_CTL, ctl_val);
-		mpam_read_monsel_reg(msc, CFG_CSU_FLT, flt_val);
-		break;
+		ret = mpam_read_monsel_reg(msc, CFG_CSU_CTL, ctl_val);
+		if (ret)
+			return ret;
+		return mpam_read_monsel_reg(msc, CFG_CSU_FLT, flt_val);
 	case mpam_feat_msmon_mbwu_31counter:
 	case mpam_feat_msmon_mbwu_44counter:
 	case mpam_feat_msmon_mbwu_63counter:
-		mpam_read_monsel_reg(msc, CFG_MBWU_CTL, ctl_val);
-		mpam_read_monsel_reg(msc, CFG_MBWU_FLT, flt_val);
-		break;
+		ret = mpam_read_monsel_reg(msc, CFG_MBWU_CTL, ctl_val);
+		if (ret)
+			return ret;
+		return mpam_read_monsel_reg(msc, CFG_MBWU_FLT, flt_val);
 	default:
 		pr_warn("Unexpected monitor type %d\n", m->type);
+		return -EINVAL;
 	}
 }
 
@@ -1246,10 +1255,11 @@ static inline void clean_msmon_ctl_val(u32 *cur_ctl)
 		*cur_ctl &= ~MSMON_CFG_MBWU_CTL_OFLOW_STATUS_L;
 }
 
-static void write_msmon_ctl_flt_vals(struct mon_read *m, u32 ctl_val,
-				     u32 flt_val)
+static int write_msmon_ctl_flt_vals(struct mon_read *m, u32 ctl_val,
+				    u32 flt_val)
 {
 	struct mpam_msc *msc = m->ris->vmsc->msc;
+	int ret;
 
 	/*
 	 * Write the ctl_val with the enable bit cleared, reset the counter,
@@ -1257,25 +1267,37 @@ static void write_msmon_ctl_flt_vals(struct mon_read *m, u32 ctl_val,
 	 */
 	switch (m->type) {
 	case mpam_feat_msmon_csu:
-		mpam_write_monsel_reg(msc, CFG_CSU_FLT, flt_val);
-		mpam_write_monsel_reg(msc, CFG_CSU_CTL, ctl_val);
-		mpam_write_monsel_reg(msc, CSU, 0);
-		mpam_write_monsel_reg(msc, CFG_CSU_CTL, ctl_val | MSMON_CFG_x_CTL_EN);
-		break;
+		ret = mpam_write_monsel_reg(msc, CFG_CSU_FLT, flt_val);
+		if (ret)
+			return ret;
+		ret = mpam_write_monsel_reg(msc, CFG_CSU_CTL, ctl_val);
+		if (ret)
+			return ret;
+		ret = mpam_write_monsel_reg(msc, CSU, 0);
+		if (ret)
+			return ret;
+		return mpam_write_monsel_reg(msc, CFG_CSU_CTL, ctl_val | MSMON_CFG_x_CTL_EN);
 	case mpam_feat_msmon_mbwu_31counter:
 	case mpam_feat_msmon_mbwu_44counter:
 	case mpam_feat_msmon_mbwu_63counter:
-		mpam_write_monsel_reg(msc, CFG_MBWU_FLT, flt_val);
-		mpam_write_monsel_reg(msc, CFG_MBWU_CTL, ctl_val);
-		mpam_write_monsel_reg(msc, CFG_MBWU_CTL, ctl_val | MSMON_CFG_x_CTL_EN);
+		ret = mpam_write_monsel_reg(msc, CFG_MBWU_FLT, flt_val);
+		if (ret)
+			return ret;
+		ret = mpam_write_monsel_reg(msc, CFG_MBWU_CTL, ctl_val);
+		if (ret)
+			return ret;
+		ret = mpam_write_monsel_reg(msc, CFG_MBWU_CTL,
+					    ctl_val | MSMON_CFG_x_CTL_EN);
+		if (ret)
+			return ret;
 		/* Counting monitors require NRDY to be reset by software */
 		if (m->type == mpam_feat_msmon_mbwu_31counter)
-			mpam_write_monsel_reg(msc, MBWU, 0);
-		else
-			mpam_msc_zero_mbwu_l(m->ris->vmsc->msc);
-		break;
+			return mpam_write_monsel_reg(msc, MBWU, 0);
+
+		return mpam_msc_zero_mbwu_l(m->ris->vmsc->msc);
 	default:
 		pr_warn("Unexpected monitor type %d\n", m->type);
+		return -EINVAL;
 	}
 }
 
-- 
2.43.0

[PATCH v4 05/10] arm_mpam: propagate MSC access errors for __ris_msmon_read()

[Andre Przywara]

Allow the function for RIS accesses to return an error, and propagate
read and write errors from the lower level up.
This function is a bit special, since it can be called via an SMP
helper, so the prototype must stay as void. So propagate any errors
using the "err" field in the struct passed in as the sole argument to
that function.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
---
 drivers/resctrl/mpam_devices.c | 36 +++++++++++++++++++++++++---------
 1 file changed, 27 insertions(+), 9 deletions(-)

diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
index 9ee4eb4db03f..bcff53477133 100644
--- a/drivers/resctrl/mpam_devices.c
+++ b/drivers/resctrl/mpam_devices.c
@@ -1328,6 +1328,10 @@ static u64 mpam_msmon_overflow_val(enum mpam_device_features type,
 	return overflow_val;
 }
 
+/*
+ * This function might be called via smp_call_function_any(), so propagate
+ * errors inside the arg struct.
+ */
 static void __ris_msmon_read(void *arg)
 {
 	u64 now;
@@ -1351,7 +1355,9 @@ static void __ris_msmon_read(void *arg)
 
 	mon_sel = FIELD_PREP(MSMON_CFG_MON_SEL_MON_SEL, ctx->mon) |
 		  FIELD_PREP(MSMON_CFG_MON_SEL_RIS, ris->ris_idx);
-	mpam_write_monsel_reg(msc, CFG_MON_SEL, mon_sel);
+	m->err = mpam_write_monsel_reg(msc, CFG_MON_SEL, mon_sel);
+	if (m->err)
+		return;
 
 	switch (m->type) {
 	case mpam_feat_msmon_mbwu_31counter:
@@ -1371,7 +1377,9 @@ static void __ris_msmon_read(void *arg)
 	 * Read the existing configuration to avoid re-writing the same values.
 	 * This saves waiting for 'nrdy' on subsequent reads.
 	 */
-	read_msmon_ctl_flt_vals(m, &cur_ctl, &cur_flt);
+	m->err = read_msmon_ctl_flt_vals(m, &cur_ctl, &cur_flt);
+	if (m->err)
+		return;
 
 	if (mpam_feat_msmon_mbwu_31counter == m->type)
 		overflow = cur_ctl & MSMON_CFG_x_CTL_OFLOW_STATUS;
@@ -1385,18 +1393,24 @@ static void __ris_msmon_read(void *arg)
 			  cur_ctl != (ctl_val | MSMON_CFG_x_CTL_EN);
 
 	if (config_mismatch || reset_on_next_read) {
-		write_msmon_ctl_flt_vals(m, ctl_val, flt_val);
+		m->err = write_msmon_ctl_flt_vals(m, ctl_val, flt_val);
+		if (m->err)
+			return;
 		overflow = false;
 	} else if (overflow) {
-		mpam_write_monsel_reg(msc, CFG_MBWU_CTL,
-				      cur_ctl &
-				      ~(MSMON_CFG_x_CTL_OFLOW_STATUS |
-					MSMON_CFG_MBWU_CTL_OFLOW_STATUS_L));
+		m->err = mpam_write_monsel_reg(msc, CFG_MBWU_CTL,
+					    cur_ctl &
+					    ~(MSMON_CFG_x_CTL_OFLOW_STATUS |
+					    MSMON_CFG_MBWU_CTL_OFLOW_STATUS_L));
+		if (m->err)
+			return;
 	}
 
 	switch (m->type) {
 	case mpam_feat_msmon_csu:
-		mpam_read_monsel_reg(msc, CSU, &now32);
+		m->err = mpam_read_monsel_reg(msc, CSU, &now32);
+		if (m->err)
+			return;
 		nrdy = now32 & MSMON___NRDY;
 		now = FIELD_GET(MSMON___VALUE, now32);
 
@@ -1418,7 +1432,9 @@ static void __ris_msmon_read(void *arg)
 			else
 				now = FIELD_GET(MSMON___L_VALUE, now);
 		} else {
-			mpam_read_monsel_reg(msc, MBWU, &now32);
+			m->err = mpam_read_monsel_reg(msc, MBWU, &now32);
+			if (m->err)
+				return;
 			nrdy = now32 & MSMON___NRDY;
 			now = FIELD_GET(MSMON___VALUE, now32);
 		}
@@ -1787,6 +1803,8 @@ static int mpam_restore_mbwu_state(void *_ris)
 			mwbu_arg.val = &val;
 
 			__ris_msmon_read(&mwbu_arg);
+			if (mwbu_arg.err)
+				return mwbu_arg.err;
 		}
 	}
 
-- 
2.43.0

[PATCH v4 06/10] arm_mpam: propagate MSC access errors for state saving function

[Andre Przywara]

Allow the mpam_save_mbwu_state() function to return an error, and
propagate read and write errors from the lower level up.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
---
 drivers/resctrl/mpam_devices.c | 29 ++++++++++++++++++++++-------
 1 file changed, 22 insertions(+), 7 deletions(-)

diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
index bcff53477133..6329443c451f 100644
--- a/drivers/resctrl/mpam_devices.c
+++ b/drivers/resctrl/mpam_devices.c
@@ -1833,22 +1833,37 @@ static int mpam_save_mbwu_state(void *arg)
 
 		mon_sel = FIELD_PREP(MSMON_CFG_MON_SEL_MON_SEL, i) |
 			  FIELD_PREP(MSMON_CFG_MON_SEL_RIS, ris->ris_idx);
-		mpam_write_monsel_reg(msc, CFG_MON_SEL, mon_sel);
-		mpam_read_monsel_reg(msc, CFG_MBWU_FLT, &cur_flt);
-		mpam_read_monsel_reg(msc, CFG_MBWU_CTL, &cur_ctl);
-		mpam_write_monsel_reg(msc, CFG_MBWU_CTL, 0);
+		ret = mpam_write_monsel_reg(msc, CFG_MON_SEL, mon_sel);
+		if (ret)
+			return ret;
+		ret = mpam_read_monsel_reg(msc, CFG_MBWU_FLT, &cur_flt);
+		if (ret)
+			return ret;
+		ret = mpam_read_monsel_reg(msc, CFG_MBWU_CTL, &cur_ctl);
+		if (ret)
+			return ret;
+		ret = mpam_write_monsel_reg(msc, CFG_MBWU_CTL, 0);
+		if (ret)
+			return ret;
 
 		if (mpam_ris_has_mbwu_long_counter(ris)) {
 			ret = mpam_msc_read_mbwu_l(msc, &val);
 			if (ret)
 				return ret;
-			mpam_msc_zero_mbwu_l(msc);
+			ret = mpam_msc_zero_mbwu_l(msc);
+			if (ret)
+				return ret;
 		} else {
 			u32 val32;
 
-			mpam_read_monsel_reg(msc, MBWU, &val32);
+			ret = mpam_read_monsel_reg(msc, MBWU, &val32);
+			if (ret)
+				return ret;
+
 			val = val32;
-			mpam_write_monsel_reg(msc, MBWU, 0);
+			ret = mpam_write_monsel_reg(msc, MBWU, 0);
+			if (ret)
+				return ret;
 		}
 
 		cfg->mon = i;
-- 
2.43.0

[PATCH v4 07/10] arm_mpam: prepare mon_sel locking for MPAM-Fb

[Andre Przywara]

The MSC MON_SEL register needs to be accessed from hardirq for the overflow
interrupt, and when taking an IPI to access these registers on platforms
where MSCs are not accesible from every CPU. This makes an irqsave
spinlock the obvious lock to protect these registers. On systems with
MPAM-Fb mailbox MSC access it must be able to sleep, meaning a mutex must
be used. So MPAM-Fb platforms cannot support an overflow interrupt easily.
Clearly these two methods can't exist for one MSC at the same time.

Change the mon_sel locking wrapper function to only use a spinlock when
the MSC is accessed directly via MMIO. In case of MPAM-Fb, we use a
mutex, but only if we are in a sleepable context. If that's not the
case, we return an error. This should not happen, as MPAM-Fb by design
does not require an MSC access to happen from a specific CPU, so there
is no need for any IPIs or preemption disabling to satisfy CPU
constraints. And since overflow interrupts are not supported at the moment
anyway, we also wouldn't meet the other case.
Bailing out early is already happening in rare occasions today.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
---
 drivers/resctrl/mpam_devices.c  |  5 ++++-
 drivers/resctrl/mpam_internal.h | 32 ++++++++++++++++++++++++++------
 2 files changed, 30 insertions(+), 7 deletions(-)

diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
index 6329443c451f..e2cb884eacf4 100644
--- a/drivers/resctrl/mpam_devices.c
+++ b/drivers/resctrl/mpam_devices.c
@@ -2225,7 +2225,10 @@ static struct mpam_msc *do_mpam_msc_drv_probe(struct platform_device *pdev)
 	if (err)
 		return ERR_PTR(err);
 
-	mpam_mon_sel_lock_init(msc);
+	err = mpam_mon_sel_lock_init(dev, msc);
+	if (err)
+		return ERR_PTR(err);
+
 	msc->id = pdev->id;
 	msc->pdev = pdev;
 	INIT_LIST_HEAD_RCU(&msc->all_msc_list);
diff --git a/drivers/resctrl/mpam_internal.h b/drivers/resctrl/mpam_internal.h
index 0c3f6a040b20..b3a6ed9ed175 100644
--- a/drivers/resctrl/mpam_internal.h
+++ b/drivers/resctrl/mpam_internal.h
@@ -126,6 +126,7 @@ struct mpam_msc {
 	 */
 	raw_spinlock_t		_mon_sel_lock;
 	unsigned long		_mon_sel_flags;
+	struct mutex		mon_sel_mutex;
 
 	void __iomem		*mapped_hwpage;
 	size_t			mapped_hwpage_sz;
@@ -139,27 +140,46 @@ struct mpam_msc {
 /* Returning false here means accesses to mon_sel must fail and report an error. */
 static inline bool __must_check mpam_mon_sel_lock(struct mpam_msc *msc)
 {
-	/* Locking will require updating to support a firmware backed interface */
-	if (WARN_ON_ONCE(msc->iface != MPAM_IFACE_MMIO))
+	if (msc->iface == MPAM_IFACE_MMIO) {
+		raw_spin_lock_irqsave(&msc->_mon_sel_lock, msc->_mon_sel_flags);
+
+		return true;
+	}
+
+	if (!preemptible())
 		return false;
 
-	raw_spin_lock_irqsave(&msc->_mon_sel_lock, msc->_mon_sel_flags);
+	mutex_lock(&msc->mon_sel_mutex);
+
 	return true;
 }
 
 static inline void mpam_mon_sel_unlock(struct mpam_msc *msc)
 {
-	raw_spin_unlock_irqrestore(&msc->_mon_sel_lock, msc->_mon_sel_flags);
+	if (msc->iface == MPAM_IFACE_MMIO) {
+		raw_spin_unlock_irqrestore(&msc->_mon_sel_lock,
+					   msc->_mon_sel_flags);
+
+		return;
+	}
+
+	mutex_unlock(&msc->mon_sel_mutex);
 }
 
 static inline void mpam_mon_sel_lock_held(struct mpam_msc *msc)
 {
-	lockdep_assert_held_once(&msc->_mon_sel_lock);
+	if (msc->iface == MPAM_IFACE_MMIO)
+		lockdep_assert_held_once(&msc->_mon_sel_lock);
+	else
+		lockdep_assert_held_once(&msc->mon_sel_mutex);
 }
 
-static inline void mpam_mon_sel_lock_init(struct mpam_msc *msc)
+static inline int mpam_mon_sel_lock_init(struct device *dev,
+					 struct mpam_msc *msc)
 {
 	raw_spin_lock_init(&msc->_mon_sel_lock);
+
+	return devm_mutex_init(dev, &msc->mon_sel_mutex);
 }
 
 DEFINE_GUARD(mon_sel,
-- 
2.43.0

[PATCH v4 08/10] arm_mpam: add MPAM-Fb MSC firmware access support

[Andre Przywara]

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  |  27 ++++-
 drivers/resctrl/mpam_fb.c       | 197 ++++++++++++++++++++++++++++++++
 drivers/resctrl/mpam_internal.h |  20 ++++
 include/linux/arm_mpam.h        |   2 +-
 5 files changed, 240 insertions(+), 8 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 e2cb884eacf4..b8108ed4b32c 100644
--- a/drivers/resctrl/mpam_devices.c
+++ b/drivers/resctrl/mpam_devices.c
@@ -181,6 +181,9 @@ 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);
+
 	*res = readl_relaxed(msc->mapped_hwpage + reg);
 
 	return 0;
@@ -197,9 +200,12 @@ 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(reg + sizeof(u32) > msc->mapped_hwpage_sz);
 	writel_relaxed(val, msc->mapped_hwpage + reg);
 
 	return 0;
@@ -1136,7 +1142,8 @@ 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);
+	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);
@@ -1485,11 +1492,16 @@ 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
@@ -1916,6 +1928,9 @@ 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..ec4bf0dd9182
--- /dev/null
+++ b/drivers/resctrl/mpam_fb.c
@@ -0,0 +1,197 @@
+// SPDX-License-Identifier: GPL-2.0
+// Copyright (C) 2024 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	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)
+
+struct mpam_fb_read_payload {
+	u32 msc_id;
+	u32 flags;
+	u32 reg_offset;
+} __packed;
+
+struct mpam_fb_write_payload {
+	u32 msc_id;
+	u32 flags;
+	u32 reg_offset;
+	u32 value;
+} __packed;
+
+#define PCC_CHAN_FLAGS_IRQ	BIT(0)
+
+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;
+
+	writel_relaxed(PCC_CHAN_FLAGS_IRQ, &pcc_shmem->flags);
+	writel_relaxed(MPAM_FB_PROT_HEADER_LEN, &pcc_shmem->length);
+	writel_relaxed(MPAM_PROTOCOL_VERSION |
+		       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 __iomem *payload = msg_buf + sizeof(*pcc_shmem);
+	int msg_size = MPAM_FB_PROT_HEADER_LEN + sizeof(*payload);
+
+	writel_relaxed(PCC_CHAN_FLAGS_IRQ, &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 __iomem *payload = msg_buf + sizeof(*pcc_shmem);
+	int msg_size = MPAM_FB_PROT_HEADER_LEN + sizeof(*payload);
+
+	writel_relaxed(PCC_CHAN_FLAGS_IRQ, &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:
+		mpam_fb_build_version_message(token, chan->shmem);
+		break;
+	}
+
+	ret = mbox_send_message(chan->mchan, NULL);
+	if (ret < 0)
+		return ret;
+
+	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)
+		return -ETIMEDOUT;
+
+	ret = readl(payload_ofs + 0x0);
+	if (ret < 0) {
+		switch (ret) {
+		case MPAM_FB_ERR_NOT_SUPPORTED:
+			return -EOPNOTSUPP;
+		case MPAM_FB_ERR_INVALID_PARAMETERS:
+			return -EINVAL;
+		case MPAM_FB_ERR_NOT_FOUND:
+			return -ENOENT;
+		case MPAM_FB_ERR_OUT_OF_RANGE:
+			return -ERANGE;
+		default:
+			return -EINVAL;
+		}
+	}
+
+	if (mpam_fb_command != MPAM_MSC_WRITE_CMD)
+		*result = readl(payload_ofs + 0x4);
+
+	return 0;
+}
+
+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);
+	if (ret)
+		return ret;
+
+	return version;
+}
diff --git a/drivers/resctrl/mpam_internal.h b/drivers/resctrl/mpam_internal.h
index b3a6ed9ed175..e4686ff0ba2e 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;
@@ -511,6 +523,14 @@ 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)
+#define MPAM_FB_MAX_MSG_SIZE	(MPAM_FB_PROT_HEADER_LEN + 4 * 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

[PATCH v4 09/10] arm_mpam: prevent MPAM-Fb accesses inside IRQ handler

[Andre Przywara]

When an MPAM MSC gets into an error condition, it can trigger an error
IRQ. We cannot really do much about those errors, but we at least query
and log the error, then disable MPAM functionality.

This error report relies on reading the MSC's error status register
(ESR) in the IRQ handler, which is not possible for MPAM-Fb based
MSC accesses, since they involve mailbox routines that might sleep.
The same is true for clearing the interrupt at the source, which
requires MSC access.

For simplicity just skip the ESR read when the MSC is not using direct
MMIO accesses, and just ignore the pending interrupts. We will wrap up
MPAM functionality regardless, knowing the exact error value will not
change that.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
---
 drivers/resctrl/mpam_devices.c | 36 +++++++++++++++++++++-------------
 1 file changed, 22 insertions(+), 14 deletions(-)

diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
index b8108ed4b32c..fea3161ffbe9 100644
--- a/drivers/resctrl/mpam_devices.c
+++ b/drivers/resctrl/mpam_devices.c
@@ -2650,25 +2650,33 @@ static irqreturn_t __mpam_irq_handler(int irq, struct mpam_msc *msc)
 					   &msc->accessibility)))
 		return IRQ_NONE;
 
-	mpam_msc_read_esr(msc, &reg);
+	/* MPAM-Fb MSC accesses cannot be done in atomic context. */
+	if (msc->iface == MPAM_IFACE_MMIO) {
+		mpam_msc_read_esr(msc, &reg);
 
-	errcode = FIELD_GET(MPAMF_ESR_ERRCODE, reg);
-	if (!errcode)
-		return IRQ_NONE;
+		errcode = FIELD_GET(MPAMF_ESR_ERRCODE, reg);
+		if (!errcode)
+			return IRQ_NONE;
 
-	/* Clear level triggered irq */
-	mpam_msc_clear_esr(msc);
+		/* Clear level triggered irq */
+		mpam_msc_clear_esr(msc);
 
-	partid = FIELD_GET(MPAMF_ESR_PARTID_MON, reg);
-	pmg = FIELD_GET(MPAMF_ESR_PMG, reg);
-	ris = FIELD_GET(MPAMF_ESR_RIS, reg);
+		partid = FIELD_GET(MPAMF_ESR_PARTID_MON, reg);
+		pmg = FIELD_GET(MPAMF_ESR_PMG, reg);
+		ris = FIELD_GET(MPAMF_ESR_RIS, reg);
 
-	pr_err_ratelimited("error irq from msc:%u '%s', partid:%u, pmg: %u, ris: %u\n",
-			   msc->id, mpam_errcode_names[errcode], partid, pmg,
-			   ris);
+		pr_err_ratelimited("error irq from msc:%u '%s', partid:%u, pmg: %u, ris: %u\n",
+				   msc->id, mpam_errcode_names[errcode], partid,
+				   pmg, ris);
 
-	/* Disable this interrupt. */
-	mpam_disable_msc_ecr(msc);
+		/* Disable this interrupt. */
+		mpam_disable_msc_ecr(msc);
+	} else {
+		struct irq_data *d = irq_get_irq_data(irq);
+
+		pr_err_ratelimited("unknown error irq %d/%ld from msc:%u\n",
+				   irq, d ? irqd_to_hwirq(d) : -1, msc->id);
+	}
 
 	/* Are we racing with the thread disabling MPAM? */
 	if (!mpam_is_enabled())
-- 
2.43.0

[PATCH v4 10/10] arm_mpam: detect and enable MPAM-Fb PCC support

[Andre Przywara]

The Arm MPAM-Fb specification [1] describes a protocol to access MSC
registers through a firmware interface. This requires a shared memory
region to hold the message, and a mailbox to trigger the access.
For ACPI this is wrapped as a PCC channel, described using existing
ACPI abstractions.

Add code to parse those PCC table descriptions associated with an MSC,
and store the parsed information in the MSC struct.
There can be multiple PCC channels, and each channel can serve multiple
MSCs, so we need to keep track of the channel usage, using a list and
a refcount.
This will be used by the MPAM-Fb access wrapper code.

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

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
---
 drivers/acpi/arm64/mpam.c      |   6 +-
 drivers/resctrl/mpam_devices.c | 127 ++++++++++++++++++++++++++++++++-
 2 files changed, 129 insertions(+), 4 deletions(-)

diff --git a/drivers/acpi/arm64/mpam.c b/drivers/acpi/arm64/mpam.c
index 84963a20c3e7..ca9b8754ae5f 100644
--- a/drivers/acpi/arm64/mpam.c
+++ b/drivers/acpi/arm64/mpam.c
@@ -220,8 +220,8 @@ static struct platform_device * __init acpi_mpam_parse_msc(struct acpi_mpam_msc_
 	struct platform_device *pdev __free(platform_device_put) =
 		platform_device_alloc("mpam_msc", tbl_msc->identifier);
 	int next_res = 0, next_prop = 0, err;
-	/* pcc, nrdy, affinity and a sentinel */
-	struct property_entry props[4] = { 0 };
+	/* pcc, msc-id, nrdy, affinity and a sentinel */
+	struct property_entry props[5] = { 0 };
 	/* mmio, 2xirq, no sentinel. */
 	struct resource res[3] = { 0 };
 	struct acpi_device *companion;
@@ -256,6 +256,8 @@ static struct platform_device * __init acpi_mpam_parse_msc(struct acpi_mpam_msc_
 	} else if (iface == MPAM_IFACE_PCC) {
 		props[next_prop++] = PROPERTY_ENTRY_U32("pcc-channel",
 							tbl_msc->base_address);
+		props[next_prop++] = PROPERTY_ENTRY_U32("msc-id",
+							tbl_msc->identifier);
 	}
 
 	acpi_mpam_parse_irqs(pdev, tbl_msc, res, &next_res);
diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
index fea3161ffbe9..fc4b5f87fbe9 100644
--- a/drivers/resctrl/mpam_devices.c
+++ b/drivers/resctrl/mpam_devices.c
@@ -19,14 +19,19 @@
 #include <linux/irqdesc.h>
 #include <linux/list.h>
 #include <linux/lockdep.h>
+#include <linux/mailbox_client.h>
 #include <linux/mutex.h>
 #include <linux/platform_device.h>
 #include <linux/printk.h>
+#include <linux/property.h>
 #include <linux/srcu.h>
 #include <linux/spinlock.h>
 #include <linux/types.h>
 #include <linux/workqueue.h>
 
+#include <acpi/pcc.h>
+#include <acpi/acpi_io.h>
+
 #include "mpam_internal.h"
 
 /* Values for the T241 errata workaround */
@@ -49,6 +54,86 @@ static LIST_HEAD(mpam_all_msc);
 
 struct srcu_struct mpam_srcu;
 
+/* PCC channels might be serving multiple MSCs, so keep a refcounted list. */
+static DEFINE_MUTEX(pcc_chan_list_lock);
+static LIST_HEAD(pcc_chan_list);
+
+static void mpam_pcc_chan_release(struct kref *ref)
+{
+	struct mpam_pcc_chan *cur = container_of(ref, struct mpam_pcc_chan,
+						 refcount);
+
+	pcc_mbox_free_channel(cur->pcc_chan);
+	list_del(&cur->pcc_chans);
+	kfree(cur);
+}
+
+static struct mpam_pcc_chan *mpam_pcc_chan_get(struct device *dev,
+					       int subspace_id)
+{
+	struct mpam_pcc_chan *cur;
+	int ret;
+
+	guard(mutex)(&pcc_chan_list_lock);
+
+	list_for_each_entry(cur, &pcc_chan_list, pcc_chans) {
+		if (cur->subspace_id == subspace_id) {
+			kref_get(&cur->refcount);
+
+			return cur;
+		}
+	}
+
+	cur = kzalloc_obj(*cur);
+	if (!cur)
+		return ERR_PTR(-ENOMEM);
+
+	cur->pcc_cl.dev = dev;
+	cur->pcc_cl.tx_block = true;
+
+	cur->pcc_chan = pcc_mbox_request_channel(&cur->pcc_cl, subspace_id);
+	if (IS_ERR(cur->pcc_chan)) {
+		long err = PTR_ERR(cur->pcc_chan);
+
+		kfree(cur);
+		return ERR_PTR(err);
+	}
+
+	/* Timeout based on the "nominal latency" from the PCC ACPI table. */
+	cur->pcc_cl.tx_tout = cur->pcc_chan->latency * 5;
+
+	ret = devm_mutex_init(dev, &cur->pcc_chan_lock);
+	if (ret)
+		return ERR_PTR(ret);
+
+	cur->subspace_id = subspace_id;
+	kref_init(&cur->refcount);
+
+	list_add_tail(&cur->pcc_chans, &pcc_chan_list);
+
+	return cur;
+}
+
+static int mpam_pcc_chan_put(struct mpam_pcc_chan *pcc_chan)
+{
+	struct mpam_pcc_chan *cur, *tmp;
+
+	if (!pcc_chan)
+		return 0;
+
+	guard(mutex)(&pcc_chan_list_lock);
+
+	list_for_each_entry_safe(cur, tmp, &pcc_chan_list, pcc_chans) {
+		if (cur == pcc_chan) {
+			kref_put(&cur->refcount, mpam_pcc_chan_release);
+
+			return 0;
+		}
+	}
+
+	return -ENOENT;
+}
+
 /*
  * Number of MSCs that have been probed. Once all MSCs have been probed MPAM
  * can be enabled.
@@ -2201,6 +2286,8 @@ static void mpam_msc_drv_remove(struct platform_device *pdev)
 {
 	struct mpam_msc *msc = platform_get_drvdata(pdev);
 
+	mpam_pcc_chan_put(msc->pcc_chan);
+
 	mutex_lock(&mpam_list_lock);
 	mpam_msc_destroy(msc);
 	mutex_unlock(&mpam_list_lock);
@@ -2211,7 +2298,7 @@ static void mpam_msc_drv_remove(struct platform_device *pdev)
 static struct mpam_msc *do_mpam_msc_drv_probe(struct platform_device *pdev)
 {
 	int err;
-	u32 tmp;
+	u32 pcc_subspace_id;
 	struct mpam_msc *msc;
 	struct resource *msc_res;
 	struct device *dev = &pdev->dev;
@@ -2259,7 +2346,8 @@ static struct mpam_msc *do_mpam_msc_drv_probe(struct platform_device *pdev)
 	if (err)
 		return ERR_PTR(err);
 
-	if (device_property_read_u32(&pdev->dev, "pcc-channel", &tmp))
+	if (device_property_read_u32(&pdev->dev, "pcc-channel",
+				     &pcc_subspace_id))
 		msc->iface = MPAM_IFACE_MMIO;
 	else
 		msc->iface = MPAM_IFACE_PCC;
@@ -2275,6 +2363,41 @@ static struct mpam_msc *do_mpam_msc_drv_probe(struct platform_device *pdev)
 		}
 		msc->mapped_hwpage_sz = msc_res->end - msc_res->start;
 		msc->mapped_hwpage = io;
+	} else if (msc->iface == MPAM_IFACE_PCC) {
+		u32 msc_id;
+		int ret;
+
+		if (device_property_read_u32(&pdev->dev, "msc-id", &msc_id)) {
+			pr_err("missing MPAM-Fb MSC identifier\n");
+			return ERR_PTR(-EINVAL);
+		}
+		msc->mpam_fb_msc_id = msc_id;
+
+		msc->pcc_chan = mpam_pcc_chan_get(&pdev->dev, pcc_subspace_id);
+		if (IS_ERR(msc->pcc_chan)) {
+			pr_err("Failed to request MSC PCC channel\n");
+			return ERR_CAST(msc->pcc_chan);
+		}
+
+		if (msc->pcc_chan->pcc_chan->shmem_size < MPAM_FB_MAX_MSG_SIZE) {
+			pr_err("MPAM-Fb PCC channel size too small.\n");
+			mpam_pcc_chan_put(msc->pcc_chan);
+			return ERR_PTR(-ENOMEM);
+		}
+		ret = mpam_fb_get_protocol_version(msc);
+		if (ret < 0) {
+			pr_err("Cannot query MPAM-Fb protocol version.\n");
+			mpam_pcc_chan_put(msc->pcc_chan);
+
+			/* ret is an MPAM-Fb error code, return a Linux one. */
+			return ERR_PTR(-EIO);
+		}
+		if ((ret >> 16) != 1) {
+			pr_err("Incompatible MPAM-Fb protocol version %d.%d\n",
+			       ret >> 16, ret & 0xffff);
+			mpam_pcc_chan_put(msc->pcc_chan);
+			return ERR_PTR(-EINVAL);
+		}
 	} else {
 		return ERR_PTR(-EINVAL);
 	}
-- 
2.43.0