[PATCH v6 28/34] arm_mpam: Consider overflow in bandwidth counter state

[Ben Horgan]

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 at huawei.com>
Reviewed-by: Gavin Shan <gshan at redhat.com>
Reviewed-by: Zeng Heng <zengheng4 at huawei.com>
Reviewed-by: Jonathan Cameron <jonathan.cameron at huawei.com>
Reviewed-by: Shaopeng Tan <tan.shaopeng at jp.fujitsu.com>
Reviewed-by: Fenghua Yu <fenghuay at nvidia.com>
Tested-by: Carl Worth <carl at os.amperecomputing.com>
Tested-by: Gavin Shan <gshan at redhat.com>
Tested-by: Zeng Heng <zengheng4 at huawei.com>
Tested-by: Shaopeng Tan <tan.shaopeng at jp.fujitsu.com>
Tested-by: Hanjun Guo <guohanjun at huawei.com>
Signed-off-by: Ben Horgan <ben.horgan at arm.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 c8ea37558f69..ecb5ecad50f8 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 12ce80bc7ff7..218e2f48c7bf 100644
--- a/drivers/resctrl/mpam_internal.h
+++ b/drivers/resctrl/mpam_internal.h
@@ -211,7 +211,8 @@ 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