linux-kernel - Re: [PATCH 29/33] arm_mpam: Probe for long/lwd mbwu counters

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Message-ID: <75cdcd36-4bd5-4ad7-a37e-9c2a195c71e5@arm.com>
Date: Thu, 28 Aug 2025 17:14:57 +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,
 devicetree@...r.kernel.org
Cc: shameerali.kolothum.thodi@...wei.com,
 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>, Rex Nie <rex.nie@...uarmicro.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>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, Catalin Marinas <catalin.marinas@....com>,
 Will Deacon <will@...nel.org>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Danilo Krummrich <dakr@...nel.org>
Subject: Re: [PATCH 29/33] arm_mpam: Probe for long/lwd mbwu counters

Hi James,

On 8/22/25 16:30, 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 have fields
> indicating support for long counters. As of now, a 44 bit counter
> represented by HAS_LONG field (bit 30) and a 63 bit counter represented
> by LWD (bit 29) can be optionally integrated. Probe for these counters
> and set corresponding feature bits if any of these counters are present.
> 
> Signed-off-by: Rohit Mathew <rohit.mathew@....com>
> Signed-off-by: James Morse <james.morse@....com>
> ---
>  drivers/resctrl/mpam_devices.c  | 23 ++++++++++++++++++++++-
>  drivers/resctrl/mpam_internal.h |  8 ++++++++
>  2 files changed, 30 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
> index 11be34b54643..2ab7f127baaa 100644
> --- a/drivers/resctrl/mpam_devices.c
> +++ b/drivers/resctrl/mpam_devices.c
> @@ -870,7 +870,7 @@ static void mpam_ris_hw_probe(struct mpam_msc_ris *ris)
>  				pr_err_once("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 mbwumonidr = mpam_read_partsel_reg(msc, MBWUMON_IDR);
nit: the variable name would be more readable with an underscore,
mwumon_idr.
>  
>  			props->num_mbwu_mon = FIELD_GET(MPAMF_MBWUMON_IDR_NUM_MON, mbwumonidr);
> @@ -880,6 +880,27 @@ static void mpam_ris_hw_probe(struct mpam_msc_ris *ris)
>  			if (FIELD_GET(MPAMF_MBWUMON_IDR_HAS_RWBW, mbwumonidr))
>  				mpam_set_feature(mpam_feat_msmon_mbwu_rwbw, props);
>  
> +			/*
> +			 * Treat long counter and its extension, lwd as mutually
> +			 * exclusive feature bits. Though these are dependent
> +			 * fields at the implementation level, there would never
> +			 * be a need for mpam_feat_msmon_mbwu_44counter (long
> +			 * counter) and mpam_feat_msmon_mbwu_63counter (lwd)
> +			 * bits to be set together.
> +			 *
> +			 * mpam_feat_msmon_mbwu isn't treated as an exclusive
> +			 * bit as this feature bit would be used as the "front
> +			 * facing feature bit" for any checks related to mbwu
> +			 * monitors.
> +			 */
> +			has_long = FIELD_GET(MPAMF_MBWUMON_IDR_HAS_LONG, mbwumonidr);
> +			if (props->num_mbwu_mon && has_long) {
> +				if (FIELD_GET(MPAMF_MBWUMON_IDR_LWD, mbwumonidr))
> +					mpam_set_feature(mpam_feat_msmon_mbwu_63counter, props);
> +				else
> +					mpam_set_feature(mpam_feat_msmon_mbwu_44counter, props);
> +			}
> +
>  			/* Is NRDY hardware managed? */
>  			mpam_mon_sel_outer_lock(msc);
>  			hw_managed = mpam_ris_hw_probe_hw_nrdy(ris, MBWU);
> diff --git a/drivers/resctrl/mpam_internal.h b/drivers/resctrl/mpam_internal.h
> index 9a50a5432f4a..9f627b5f72a1 100644
> --- a/drivers/resctrl/mpam_internal.h
> +++ b/drivers/resctrl/mpam_internal.h
> @@ -178,7 +178,15 @@ enum mpam_device_features {
>  	mpam_feat_msmon_csu,
>  	mpam_feat_msmon_csu_capture,
>  	mpam_feat_msmon_csu_hw_nrdy,
> +
> +	/*
> +	 * Having mpam_feat_msmon_mbwu set doesn't mean the regular 31 bit MBWU
> +	 * counter would be used. The exact counter used is decided based on the
> +	 * status of mpam_feat_msmon_mbwu_l/mpam_feat_msmon_mbwu_lwd as well.
mpam_feat_msmon_mbwu_44counter/mpam_feat_msmon_mbwu_63counter
> +	 */
>  	mpam_feat_msmon_mbwu,
> +	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,

Other than the two nits, the change looks good to me.

Reviewed-by: Ben Horgan <ben.horgan@....com>

Thanks,

Ben