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Message-ID: <9dbc4e1a-d614-4427-a7e8-066a3e29055e@arm.com>
Date: Thu, 6 Nov 2025 15:43:28 +0000
From: Ben Horgan <ben.horgan@....com>
To: Peter Newman <peternewman@...gle.com>, 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>
Subject: Re: [PATCH v3 26/29] arm_mpam: Use long MBWU counters if supported
Hi Peter,
On 11/6/25 15:18, Peter Newman wrote:
> 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;
> }
>
Yes, this looks like a correct change to me.
[...]
>> 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.
Good spot. I think we can just move the 'if' further up. I'll make these
changes when I do the repost for James.
>
> Thanks,
> -Peter
Thanks,
Ben
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