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Message-ID: <CALPaoCgO+NW9Hnb0x-eL7oR-Yj75V14hOW=LxAEYUEeK9SMCUA@mail.gmail.com>
Date: Thu, 6 Nov 2025 16:18:47 +0100
From: Peter Newman <peternewman@...gle.com>
To: James Morse <james.morse@....com>
Cc: linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
linux-acpi@...r.kernel.org,
D Scott Phillips OS <scott@...amperecomputing.com>, carl@...amperecomputing.com,
lcherian@...vell.com, bobo.shaobowang@...wei.com, tan.shaopeng@...itsu.com,
baolin.wang@...ux.alibaba.com, Jamie Iles <quic_jiles@...cinc.com>,
Xin Hao <xhao@...ux.alibaba.com>, dfustini@...libre.com, amitsinght@...vell.com,
David Hildenbrand <david@...hat.com>, Dave Martin <dave.martin@....com>, Koba Ko <kobak@...dia.com>,
Shanker Donthineni <sdonthineni@...dia.com>, fenghuay@...dia.com, baisheng.gao@...soc.com,
Jonathan Cameron <jonathan.cameron@...wei.com>, Rob Herring <robh@...nel.org>,
Rohit Mathew <rohit.mathew@....com>, Rafael Wysocki <rafael@...nel.org>, Len Brown <lenb@...nel.org>,
Lorenzo Pieralisi <lpieralisi@...nel.org>, Hanjun Guo <guohanjun@...wei.com>,
Sudeep Holla <sudeep.holla@....com>, Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will@...nel.org>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Danilo Krummrich <dakr@...nel.org>, Jeremy Linton <jeremy.linton@....com>, Gavin Shan <gshan@...hat.com>,
Ben Horgan <ben.horgan@....com>
Subject: Re: [PATCH v3 26/29] arm_mpam: Use long MBWU counters if supported
Hi James,
On Fri, Oct 17, 2025 at 8:59 PM James Morse <james.morse@....com> wrote:
>
> From: Rohit Mathew <rohit.mathew@....com>
>
> Now that the larger counter sizes are probed, make use of them.
>
> Callers of mpam_msmon_read() may not know (or care!) about the different
> counter sizes. Allow them to specify mpam_feat_msmon_mbwu and have the
> driver pick the counter to use.
>
> Only 32bit accesses to the MSC are required to be supported by the
> spec, but these registers are 64bits. The lower half may overflow
> into the higher half between two 32bit reads. To avoid this, use
> a helper that reads the top half multiple times to check for overflow.
>
> Signed-off-by: Rohit Mathew <rohit.mathew@....com>
> [morse: merged multiple patches from Rohit, added explicit counter selection ]
> Signed-off-by: James Morse <james.morse@....com>
> Reviewed-by: Ben Horgan <ben.horgan@....com>
> Reviewed-by: Jonathan Cameron <jonathan.cameron@...wei.com>
> Reviewed-by: Fenghua Yu <fenghuay@...dia.com>
> Tested-by: Fenghua Yu <fenghuay@...dia.com>
> ---
> Changes since v2:
> * Removed mpam_feat_msmon_mbwu as a top-level bit for explicit 31bit counter
> selection.
> * Allow callers of mpam_msmon_read() to specify mpam_feat_msmon_mbwu and have
> the driver pick a supported counter size.
> * Rephrased commit message.
>
> Changes since v1:
> * Only clear OFLOW_STATUS_L on MBWU counters.
>
> Changes since RFC:
> * Commit message wrangling.
> * Refer to 31 bit counters as opposed to 32 bit (registers).
> ---
> drivers/resctrl/mpam_devices.c | 134 ++++++++++++++++++++++++++++-----
> 1 file changed, 116 insertions(+), 18 deletions(-)
>
> diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
> index f4d07234ce10..c207a6d2832c 100644
> --- a/drivers/resctrl/mpam_devices.c
> +++ b/drivers/resctrl/mpam_devices.c
> @@ -897,6 +897,48 @@ struct mon_read {
> int err;
> };
>
> +static bool mpam_ris_has_mbwu_long_counter(struct mpam_msc_ris *ris)
> +{
> + return (mpam_has_feature(mpam_feat_msmon_mbwu_63counter, &ris->props) ||
> + mpam_has_feature(mpam_feat_msmon_mbwu_44counter, &ris->props));
> +}
> +
> +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;
> +
> + 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);
> + 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);
> +
> + 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 MSMON___NRDY_L;
> +}
> +
> +static void 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));
> +
> + __mpam_write_reg(msc, MSMON_MBWU_L, 0);
> + __mpam_write_reg(msc, MSMON_MBWU_L + 4, 0);
> +}
> +
> static void gen_msmon_ctl_flt_vals(struct mon_read *m, u32 *ctl_val,
> u32 *flt_val)
> {
> @@ -924,7 +966,9 @@ static void gen_msmon_ctl_flt_vals(struct mon_read *m, u32 *ctl_val,
> ctx->csu_exclude_clean);
>
> break;
> - case mpam_feat_msmon_mbwu:
> + case mpam_feat_msmon_mbwu_31counter:
> + case mpam_feat_msmon_mbwu_44counter:
> + case mpam_feat_msmon_mbwu_63counter:
> *ctl_val |= MSMON_CFG_MBWU_CTL_TYPE_MBWU;
>
> if (mpam_has_feature(mpam_feat_msmon_mbwu_rwbw, &m->ris->props))
> @@ -946,7 +990,9 @@ static void read_msmon_ctl_flt_vals(struct mon_read *m, u32 *ctl_val,
> *ctl_val = mpam_read_monsel_reg(msc, CFG_CSU_CTL);
> *flt_val = mpam_read_monsel_reg(msc, CFG_CSU_FLT);
> return;
> - case mpam_feat_msmon_mbwu:
> + 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);
> return;
> @@ -959,6 +1005,9 @@ static void read_msmon_ctl_flt_vals(struct mon_read *m, u32 *ctl_val,
> static void clean_msmon_ctl_val(u32 *cur_ctl)
> {
> *cur_ctl &= ~MSMON_CFG_x_CTL_OFLOW_STATUS;
> +
> + if (FIELD_GET(MSMON_CFG_x_CTL_TYPE, *cur_ctl) == MSMON_CFG_MBWU_CTL_TYPE_MBWU)
> + *cur_ctl &= ~MSMON_CFG_MBWU_CTL_OFLOW_STATUS_L;
> }
>
> static void write_msmon_ctl_flt_vals(struct mon_read *m, u32 ctl_val,
> @@ -978,10 +1027,15 @@ static void write_msmon_ctl_flt_vals(struct mon_read *m, u32 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;
> - case mpam_feat_msmon_mbwu:
> + case mpam_feat_msmon_mbwu_44counter:
> + case mpam_feat_msmon_mbwu_63counter:
> + mpam_msc_zero_mbwu_l(m->ris->vmsc->msc);
> + fallthrough;
> + case mpam_feat_msmon_mbwu_31counter:
> 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, MBWU, 0);
> +
> mpam_write_monsel_reg(msc, CFG_MBWU_CTL, ctl_val | MSMON_CFG_x_CTL_EN);
>
> mbwu_state = &m->ris->mbwu_state[m->ctx->mon];
> @@ -993,10 +1047,19 @@ static void write_msmon_ctl_flt_vals(struct mon_read *m, u32 ctl_val,
> }
> }
>
> -static u64 mpam_msmon_overflow_val(struct mpam_msc_ris *ris)
> +static u64 mpam_msmon_overflow_val(enum mpam_device_features type)
> {
> - /* TODO: scaling, and long counters */
> - return GENMASK_ULL(30, 0);
> + /* TODO: implement scaling counters */
> + switch (type) {
> + case mpam_feat_msmon_mbwu_63counter:
> + return GENMASK_ULL(62, 0);
> + case mpam_feat_msmon_mbwu_44counter:
> + return GENMASK_ULL(43, 0);
> + case mpam_feat_msmon_mbwu_31counter:
> + return GENMASK_ULL(30, 0);
> + default:
> + return 0;
> + }
> }
>
> /* Call with MSC lock held */
> @@ -1037,11 +1100,24 @@ static void __ris_msmon_read(void *arg)
> nrdy = now & MSMON___NRDY;
> now = FIELD_GET(MSMON___VALUE, now);
> break;
> - case mpam_feat_msmon_mbwu:
> - now = mpam_read_monsel_reg(msc, MBWU);
> - if (mpam_has_feature(mpam_feat_msmon_mbwu_hw_nrdy, rprops))
> - nrdy = now & MSMON___NRDY;
> - now = FIELD_GET(MSMON___VALUE, now);
> + case mpam_feat_msmon_mbwu_31counter:
> + case mpam_feat_msmon_mbwu_44counter:
> + case mpam_feat_msmon_mbwu_63counter:
Should you check for one of these three features instead of
mpam_feat_msmon_mbwu further up in this function when checking for
reset_on_next_read?
- if (m->type == mpam_feat_msmon_mbwu) {
+ switch (m->type) {
+ case mpam_feat_msmon_mbwu_31counter:
+ case mpam_feat_msmon_mbwu_44counter:
+ case mpam_feat_msmon_mbwu_63counter:
mbwu_state = &ris->mbwu_state[ctx->mon];
if (mbwu_state) {
reset_on_next_read = mbwu_state->reset_on_next_read;
mbwu_state->reset_on_next_read = false;
}
+ break;
+ default:
+ break;
}
> + if (m->type != mpam_feat_msmon_mbwu_31counter) {
> + now = mpam_msc_read_mbwu_l(msc);
> + if (mpam_has_feature(mpam_feat_msmon_mbwu_hw_nrdy, rprops))
> + nrdy = now & MSMON___NRDY_L;
> +
> + if (m->type == mpam_feat_msmon_mbwu_63counter)
> + now = FIELD_GET(MSMON___LWD_VALUE, now);
> + else
> + now = FIELD_GET(MSMON___L_VALUE, now);
> + } else {
> + now = mpam_read_monsel_reg(msc, MBWU);
> + if (mpam_has_feature(mpam_feat_msmon_mbwu_hw_nrdy, rprops))
> + nrdy = now & MSMON___NRDY;
> + now = FIELD_GET(MSMON___VALUE, now);
> + }
>
> if (nrdy)
> break;
> @@ -1050,7 +1126,7 @@ static void __ris_msmon_read(void *arg)
>
> /* Add any pre-overflow value to the mbwu_state->val */
> if (mbwu_state->prev_val > now)
> - overflow_val = mpam_msmon_overflow_val(ris) - mbwu_state->prev_val;
> + overflow_val = mpam_msmon_overflow_val(m->type) - mbwu_state->prev_val;
>
> mbwu_state->prev_val = now;
> mbwu_state->correction += overflow_val;
> @@ -1106,13 +1182,26 @@ static int _msmon_read(struct mpam_component *comp, struct mon_read *arg)
> return any_err;
> }
>
> +static enum mpam_device_features mpam_msmon_choose_counter(struct mpam_class *class)
> +{
> + struct mpam_props *cprops = &class->props;
> +
> + if (mpam_has_feature(mpam_feat_msmon_mbwu_44counter, cprops))
> + return mpam_feat_msmon_mbwu_44counter;
> + if (mpam_has_feature(mpam_feat_msmon_mbwu_63counter, cprops))
> + return mpam_feat_msmon_mbwu_63counter;
> +
> + return mpam_feat_msmon_mbwu_31counter;
> +}
> +
> int mpam_msmon_read(struct mpam_component *comp, struct mon_cfg *ctx,
> enum mpam_device_features type, u64 *val)
> {
> int err;
> struct mon_read arg;
> u64 wait_jiffies = 0;
> - struct mpam_props *cprops = &comp->class->props;
> + struct mpam_class *class = comp->class;
> + struct mpam_props *cprops = &class->props;
>
> might_sleep();
>
> @@ -1129,9 +1218,12 @@ int mpam_msmon_read(struct mpam_component *comp, struct mon_cfg *ctx,
> };
> *val = 0;
>
> + if (type == mpam_feat_msmon_mbwu)
> + type = mpam_msmon_choose_counter(class);
`type` was already recorded in arg->type, so the result of this lookup
will be ignored on the first call to _msmon_read()
If mpam_feat_msmon_mbwu can somehow still result in -EBUSY, then the
repeat call may use the right type.
Thanks,
-Peter
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