[PATCH 05/27] arm_mpam: Ensure MBWU counters are reset on restore

[James Morse]

From: Ben Horgan <ben.horgan at arm.com>

When an MSC becomes inaccessible due to cpu offline CFG_MBWU_CTL is set to
zero in mpam_save_mbwu_state(). This is very likely to mean that the config
will mismatch when restoring and so the monitor will be reset. However, the
state may have been lost and so there are no guarantees. Ensure the reset
happens by setting the reset_on_next_read and remove the unnecessary writes
from mpam_save_mbwu_state().

Fixes: 41e8a14950e1 ("arm_mpam: Track bandwidth counter state for power management")
Signed-off-by: Ben Horgan <ben.horgan at arm.com>
Tested-by: Gavin Shan <gshan at redhat.com>
Reviewed-by: Gavin Shan <gshan at redhat.com>
Reviewed-by: James Morse <james.morse at arm.com>
[morse: Restored clearing of CTL register for kexec/powerdown]
Signed-off-by: James Morse <james.morse at arm.com>
---
 drivers/resctrl/mpam_devices.c | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
index d39d210574a6..6df48bec82e2 100644
--- a/drivers/resctrl/mpam_devices.c
+++ b/drivers/resctrl/mpam_devices.c
@@ -1652,6 +1652,7 @@ static int mpam_restore_mbwu_state(void *_ris)
 	u64 val;
 	struct mon_read mwbu_arg;
 	struct mpam_msc_ris *ris = _ris;
+	struct msmon_mbwu_state *mbwu_state;
 	struct mpam_msc *msc = ris->vmsc->msc;
 	struct mpam_class *class = ris->vmsc->comp->class;
 
@@ -1659,16 +1660,20 @@ static int mpam_restore_mbwu_state(void *_ris)
 		if (WARN_ON_ONCE(!mpam_mon_sel_lock(msc)))
 			return -EIO;
 
-		if (!ris->mbwu_state[i].enabled) {
+		mbwu_state = &ris->mbwu_state[i];
+
+		if (!mbwu_state->enabled) {
 			mpam_mon_sel_unlock(msc);
 			continue;
 		}
 
 		mwbu_arg.ris = ris;
-		mwbu_arg.ctx = &ris->mbwu_state[i].cfg;
+		mwbu_arg.ctx = &mbwu_state->cfg;
 		mwbu_arg.type = mpam_msmon_choose_counter(class);
 		mwbu_arg.val = &val;
 
+		mbwu_state->reset_on_next_read = true;
+
 		mpam_mon_sel_unlock(msc);
 
 		__ris_msmon_read(&mwbu_arg);
@@ -1703,13 +1708,10 @@ static int mpam_save_mbwu_state(void *arg)
 		cur_ctl = mpam_read_monsel_reg(msc, CFG_MBWU_CTL);
 		mpam_write_monsel_reg(msc, CFG_MBWU_CTL, 0);
 
-		if (mpam_ris_has_mbwu_long_counter(ris)) {
+		if (mpam_ris_has_mbwu_long_counter(ris))
 			val = mpam_msc_read_mbwu_l(msc);
-			mpam_msc_zero_mbwu_l(msc);
-		} else {
+		else
 			val = mpam_read_monsel_reg(msc, MBWU);
-			mpam_write_monsel_reg(msc, MBWU, 0);
-		}
 
 		cfg->mon = i;
 		cfg->pmg = FIELD_GET(MSMON_CFG_x_FLT_PMG, cur_flt);
-- 
2.53.0