linux-kernel - Re: [PATCH v3 25/29] arm_mpam: Probe for long/lwd mbwu counters

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Message-ID: <c33c16dc-a955-41f9-9fb2-1397f056cb00@arm.com>
Date: Wed, 22 Oct 2025 12:23:15 +0100
From: Ben Horgan <ben.horgan@....com>
To: James Morse <james.morse@....com>, linux-kernel@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, linux-acpi@...r.kernel.org
Cc: 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>, peternewman@...gle.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 25/29] arm_mpam: Probe for long/lwd mbwu counters

Hi James,

On 10/17/25 19:56, James Morse wrote:
> From: Rohit Mathew <rohit.mathew@....com>
> 
> mpam v0.1 and versions above v1.0 support optional long counter for
> memory bandwidth monitoring. The MPAMF_MBWUMON_IDR register has fields
> indicating support for long counters.
> 
> Probe these feature bits.
> 
> The mpam_feat_msmon_mbwu feature is used to indicate that bandwidth
> monitors are supported, instead of muddling this with which size of
> bandwidth monitors, add an explicit 31 bit counter feature.
> 
> Signed-off-by: Rohit Mathew <rohit.mathew@....com>
> [ morse: Added 31bit counter feature to simplify later logic ]
> Signed-off-by: James Morse <james.morse@....com>
> Reviewed-by: Ben Horgan <ben.horgan@....com>
> Tested-by: Fenghua Yu <fenghuay@...dia.com>
> ---
> Changes since v2:
>  * Added 31 bit counter type feature.
>  * Altered commit message.
> ---
>  drivers/resctrl/mpam_devices.c  | 13 +++++++++++--
>  drivers/resctrl/mpam_internal.h |  3 +++
>  2 files changed, 14 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
> index deb1dcc6f6b1..f4d07234ce10 100644
> --- a/drivers/resctrl/mpam_devices.c
> +++ b/drivers/resctrl/mpam_devices.c
> @@ -777,16 +777,25 @@ static void mpam_ris_hw_probe(struct mpam_msc_ris *ris)
>  				dev_err_once(dev, "Counters are not usable because not-ready timeout was not provided by firmware.");
>  		}
>  		if (FIELD_GET(MPAMF_MSMON_IDR_MSMON_MBWU, msmon_features)) {
> -			bool hw_managed;
> +			bool has_long, hw_managed;
>  			u32 mbwumon_idr = mpam_read_partsel_reg(msc, MBWUMON_IDR);
>  
>  			props->num_mbwu_mon = FIELD_GET(MPAMF_MBWUMON_IDR_NUM_MON, mbwumon_idr);
> -			if (props->num_mbwu_mon)
> +			if (props->num_mbwu_mon) {
>  				mpam_set_feature(mpam_feat_msmon_mbwu, props);
> +				mpam_set_feature(mpam_feat_msmon_mbwu_31counter, props);
> +			}
>  
>  			if (FIELD_GET(MPAMF_MBWUMON_IDR_HAS_RWBW, mbwumon_idr))
>  				mpam_set_feature(mpam_feat_msmon_mbwu_rwbw, props);
>  
> +			has_long = FIELD_GET(MPAMF_MBWUMON_IDR_HAS_LONG, mbwumon_idr);
> +			if (props->num_mbwu_mon && has_long) {
> +				mpam_set_feature(mpam_feat_msmon_mbwu_44counter, props);
> +				if (FIELD_GET(MPAMF_MBWUMON_IDR_LWD, mbwumon_idr))
> +					mpam_set_feature(mpam_feat_msmon_mbwu_63counter, props);
> +			}
> +

I think it's clearer to set each mpam_feat_msmon_mbwu_XXcounter for just
the size of counter the hardware supports rather than all XX up to that
size.

>  			/* Is NRDY hardware managed? */
>  			hw_managed = mpam_ris_hw_probe_hw_nrdy(ris, MBWU);
>  			if (hw_managed)
> diff --git a/drivers/resctrl/mpam_internal.h b/drivers/resctrl/mpam_internal.h
> index 28c475d18d86..ff38b4bbfc2b 100644
> --- a/drivers/resctrl/mpam_internal.h
> +++ b/drivers/resctrl/mpam_internal.h
> @@ -158,6 +158,9 @@ enum mpam_device_features {
>  	mpam_feat_msmon_csu_xcl,
>  	mpam_feat_msmon_csu_hw_nrdy,
>  	mpam_feat_msmon_mbwu,
> +	mpam_feat_msmon_mbwu_31counter,
> +	mpam_feat_msmon_mbwu_44counter,
> +	mpam_feat_msmon_mbwu_63counter,
>  	mpam_feat_msmon_mbwu_capture,
>  	mpam_feat_msmon_mbwu_rwbw,
>  	mpam_feat_msmon_mbwu_hw_nrdy,

-- 
Thanks,

Ben