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: <20250912132229.000044c7@huawei.com>
Date: Fri, 12 Sep 2025 13:22:29 +0100
From: Jonathan Cameron <jonathan.cameron@...wei.com>
To: James Morse <james.morse@....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

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.
> 
> CC: Dave Martin <Dave.Martin@....com>
> Signed-off-by: James Morse <james.morse@....com>
Trivial comments
Reviewed-by: Jonathan Cameron <jonathan.cameron@...wei.com>

> +
> +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,
	};
> +
> +	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.

> +	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.

Jonathan