linux-kernel - Re: [PATCH v2 20/29] arm_mpam: Allow configuration to be applied and restored during cpu online

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Message-ID: <4aec304d-4a89-4957-ac72-148db39f6117@arm.com>
Date: Tue, 7 Oct 2025 12:11:09 +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 20/29] arm_mpam: Allow configuration to be applied and
 restored during cpu online

Hi Jonathan,

On 12/09/2025 13:22, Jonathan Cameron wrote:
> On Wed, 10 Sep 2025 20:43:00 +0000
> James Morse <james.morse@....com> wrote:
> 
>> When CPUs come online the MSC's original configuration should be restored.
>>
>> Add struct mpam_config to hold the configuration. This has a bitmap of
>> features that were modified. Once the maximum partid is known, allocate
>> a configuration array for each component, and reprogram each RIS
>> configuration from this.

> Trivial comments
> Reviewed-by: Jonathan Cameron <jonathan.cameron@...wei.com>

Thanks!


>> +static void mpam_init_reset_cfg(struct mpam_config *reset_cfg)
>> +{
>> +	memset(reset_cfg, 0, sizeof(*reset_cfg));
> 
> Might as well do the following and skip the memset.
> 
> 	*reset_cfg = (struct mpam_config) {
> 		.features = ~0,
> 		.cpbm = ~0,
> 		.mbw_pbm = ~0,
> 		.mbw_max = MPAM...
> 		.reset_cpbm = true,
> 		.reset_mbw_pbm = true,
> 	};

Sure,


>> +	reset_cfg->features = ~0;
>> +	reset_cfg->cpbm = ~0;
>> +	reset_cfg->mbw_pbm = ~0;
>> +	reset_cfg->mbw_max = MPAMCFG_MBW_MAX_MAX;
>> +
>> +	reset_cfg->reset_cpbm = true;
>> +	reset_cfg->reset_mbw_pbm = true;
>> +}
> 
>> +static int mpam_allocate_config(void)
>> +{
>> +	int err = 0;
> 
> Always set before use. Maybe push down so it is in tighter scope and
> can declare and initialize to final value in one line.

Sure,


>> +	struct mpam_class *class;
>> +	struct mpam_component *comp;
>> +
>> +	lockdep_assert_held(&mpam_list_lock);
>> +
>> +	list_for_each_entry(class, &mpam_classes, classes_list) {
>> +		list_for_each_entry(comp, &class->components, class_list) {
>> +			err = __allocate_component_cfg(comp);
>> +			if (err)
>> +				return err;
>> +		}
>> +	}
>> +
>> +	return 0;
>> +}
> 
> 
>> diff --git a/drivers/resctrl/mpam_internal.h b/drivers/resctrl/mpam_internal.h
>> index b69fa9199cb4..17570d9aae9b 100644
>> --- a/drivers/resctrl/mpam_internal.h
>> +++ b/drivers/resctrl/mpam_internal.h
>> @@ -169,11 +169,7 @@ struct mpam_props {
>>  	u16			num_mbwu_mon;
>>  };
>>  
>> -static inline bool mpam_has_feature(enum mpam_device_features feat,
>> -				    struct mpam_props *props)
>> -{
>> -	return (1 << feat) & props->features;
>> -}
>> +#define mpam_has_feature(_feat, x)	((1 << (_feat)) & (x)->features)
> 
> If this is worth doing push it back to original introduction.
> I'm not sure it is necessary.

It's the change in this patch that makes it necessary, maybe_update_config() goes calling
mpam_has_feature() on a configuration instead of a class/msc/ris props structure. I could
have made that a separate helper to get the type right - but making it a macro was simpler.

I'll push it back earlier.


Thanks,

James