linux-kernel - Re: [PATCH v2 13/29] arm_mpam: Probe the hardware features resctrl supports

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Message-ID: <fea6066e-b94d-4ac1-9a33-3e42a8923de6@arm.com>
Date: Mon, 29 Sep 2025 18:45:01 +0100
From: James Morse <james.morse@....com>
To: Jonathan Cameron <jonathan.cameron@...wei.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>, 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, 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>
Subject: Re: [PATCH v2 13/29] arm_mpam: Probe the hardware features resctrl
 supports

Hi Jonathan,

On 11/09/2025 16:29, Jonathan Cameron wrote:
> On Wed, 10 Sep 2025 20:42:53 +0000
> James Morse <james.morse@....com> wrote:
> 
>> Expand the probing support with the control and monitor types
>> we can use with resctrl.
>>
>> CC: Dave Martin <Dave.Martin@....com>
>> Signed-off-by: James Morse <james.morse@....com>
> 
> A few trivial things inline.
> LGTM
> Reviewed-by: Jonathan Cameron <jonathan.cameron@...wei.com>

Thanks!


>> @@ -592,6 +736,7 @@ static int mpam_msc_hw_probe(struct mpam_msc *msc)
>>  	mutex_lock(&msc->part_sel_lock);
>>  	idr = mpam_msc_read_idr(msc);
>>  	mutex_unlock(&msc->part_sel_lock);
>> +
> Stray change  - push it to earlier patch.

Fixed,


>> diff --git a/drivers/resctrl/mpam_internal.h b/drivers/resctrl/mpam_internal.h
>> index 4cc44d4e21c4..5ae5d4eee8ec 100644
>> --- a/drivers/resctrl/mpam_internal.h
>> +++ b/drivers/resctrl/mpam_internal.h
>> @@ -112,6 +112,55 @@ static inline void mpam_mon_sel_lock_init(struct mpam_msc *msc)
>>  	raw_spin_lock_init(&msc->_mon_sel_lock);
>>  }
>>  
>> +/*
>> + * When we compact the supported features, we don't care what they are.
>> + * Storing them as a bitmap makes life easy.
>> + */
>> +typedef u16 mpam_features_t;
> 
> Maybe use a bitmap type and avoid the need to be careful on sizing etc?

That would be unsigned long at a minimum, which is four times larger than needed.
As there is a build-time check, I'm not worried about this ever being wrong...


>> +
>> +/* Bits for mpam_features_t */
>> +enum mpam_device_features {
>> +	mpam_feat_ccap_part = 0,
>> +	mpam_feat_cpor_part,
>> +	mpam_feat_mbw_part,
>> +	mpam_feat_mbw_min,
>> +	mpam_feat_mbw_max,
>> +	mpam_feat_mbw_prop,
>> +	mpam_feat_msmon,
>> +	mpam_feat_msmon_csu,
>> +	mpam_feat_msmon_csu_capture,
>> +	mpam_feat_msmon_csu_hw_nrdy,
>> +	mpam_feat_msmon_mbwu,
>> +	mpam_feat_msmon_mbwu_capture,
>> +	mpam_feat_msmon_mbwu_rwbw,
>> +	mpam_feat_msmon_mbwu_hw_nrdy,
>> +	mpam_feat_msmon_capt,
>> +	MPAM_FEATURE_LAST,
> 
> If it's always meant to be LAST, I'd drop the trailing comma.

Sure. Full-stops for enums!


Thanks,

James