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

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Message-ID: <80fab62a-9043-4490-8eb9-f7ab760ef9ac@arm.com>
Date: Wed, 10 Sep 2025 20:30:39 +0100
From: James Morse <james.morse@....com>
To: Ben Horgan <ben.horgan@....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 Ben,

On 28/08/2025 17:14, Ben Horgan wrote:
> 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.

>> 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.

Sure,


>>  
>>  			props->num_mbwu_mon = FIELD_GET(MPAMF_MBWUMON_IDR_NUM_MON, mbwumonidr);

>> 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

That's my fault - I hate the names for these things!


>> +	 */
>>  	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!

James