linux-kernel - [PATCH v5 28/34] arm_mpam: Consider overflow in bandwidth counter state

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Message-ID: <20251117170014.4113754-29-ben.horgan@arm.com>
Date: Mon, 17 Nov 2025 17:00:07 +0000
From: Ben Horgan <ben.horgan@....com>
To: james.morse@....com
Cc: amitsinght@...vell.com,
	baisheng.gao@...soc.com,
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	Ben Horgan <ben.horgan@....com>,
	Zeng Heng <zengheng4@...wei.com>
Subject: [PATCH v5 28/34] arm_mpam: Consider overflow in bandwidth counter state

Use the overflow status bit to track overflow on each bandwidth counter
read and add the counter size to the correction when overflow is detected.

This assumes that only a single overflow has occurred since the last read
of the counter. Overflow interrupts, on hardware that supports them could
be used to remove this limitation.

Cc: Zeng Heng <zengheng4@...wei.com>
Reviewed-by: Gavin Shan <gshan@...hat.com>
Reviewed-by: Zeng Heng <zengheng4@...wei.com>
Reviewed-by: Jonathan Cameron <jonathan.cameron@...wei.com>
Tested-by: Carl Worth <carl@...amperecomputing.com>
Tested-by: Gavin Shan <gshan@...hat.com>
Tested-by: Zeng Heng <zengheng4@...wei.com>
Signed-off-by: Ben Horgan <ben.horgan@....com>
---
 drivers/resctrl/mpam_devices.c  | 24 ++++++++++++++++++++++--
 drivers/resctrl/mpam_internal.h |  3 ++-
 2 files changed, 24 insertions(+), 3 deletions(-)

diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
index 7983d492ad9a..1adc55d258ab 100644
--- a/drivers/resctrl/mpam_devices.c
+++ b/drivers/resctrl/mpam_devices.c
@@ -985,11 +985,18 @@ static void write_msmon_ctl_flt_vals(struct mon_read *m, u32 ctl_val,
 	}
 }
 
+static u64 mpam_msmon_overflow_val(enum mpam_device_features type)
+{
+	/* TODO: scaling, and long counters */
+	return BIT_ULL(hweight_long(MSMON___VALUE));
+}
+
 static void __ris_msmon_read(void *arg)
 {
 	u64 now;
 	bool nrdy = false;
 	bool config_mismatch;
+	bool overflow;
 	struct mon_read *m = arg;
 	struct mon_cfg *ctx = m->ctx;
 	struct mpam_msc_ris *ris = m->ris;
@@ -1011,13 +1018,20 @@ static void __ris_msmon_read(void *arg)
 	 * This saves waiting for 'nrdy' on subsequent reads.
 	 */
 	read_msmon_ctl_flt_vals(m, &cur_ctl, &cur_flt);
+	overflow = cur_ctl & MSMON_CFG_x_CTL_OFLOW_STATUS;
+
 	clean_msmon_ctl_val(&cur_ctl);
 	gen_msmon_ctl_flt_vals(m, &ctl_val, &flt_val);
 	config_mismatch = cur_flt != flt_val ||
 			  cur_ctl != (ctl_val | MSMON_CFG_x_CTL_EN);
 
-	if (config_mismatch)
+	if (config_mismatch) {
 		write_msmon_ctl_flt_vals(m, ctl_val, flt_val);
+		overflow = false;
+	} else if (overflow) {
+		mpam_write_monsel_reg(msc, CFG_MBWU_CTL,
+				      cur_ctl & ~MSMON_CFG_x_CTL_OFLOW_STATUS);
+	}
 
 	switch (m->type) {
 	case mpam_feat_msmon_csu:
@@ -1037,7 +1051,13 @@ static void __ris_msmon_read(void *arg)
 
 		mbwu_state = &ris->mbwu_state[ctx->mon];
 
-		/* Include bandwidth consumed before the last hardware reset */
+		if (overflow)
+			mbwu_state->correction += mpam_msmon_overflow_val(m->type);
+
+		/*
+		 * Include bandwidth consumed before the last hardware reset and
+		 * a counter size increment for each overflow.
+		 */
 		now += mbwu_state->correction;
 		break;
 	default:
diff --git a/drivers/resctrl/mpam_internal.h b/drivers/resctrl/mpam_internal.h
index 9c140d8b1e0d..41f30b1a0d97 100644
--- a/drivers/resctrl/mpam_internal.h
+++ b/drivers/resctrl/mpam_internal.h
@@ -209,7 +209,8 @@ struct msmon_mbwu_state {
 	struct mon_cfg	cfg;
 
 	/*
-	 * The value to add to the new reading to account for power management.
+	 * The value to add to the new reading to account for power management,
+	 * and overflow.
 	 */
 	u64		correction;
 
-- 
2.43.0