linux-kernel - Re: [PATCH v2 17/45] arm_mpam: resctrl: Pick the caches we will use as resctrl resources

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Message-ID: <20260105174631.000043f3@huawei.com>
Date: Mon, 5 Jan 2026 17:46:31 +0000
From: Jonathan Cameron <jonathan.cameron@...wei.com>
To: Ben Horgan <ben.horgan@....com>
CC: <amitsinght@...vell.com>, <baisheng.gao@...soc.com>,
	<baolin.wang@...ux.alibaba.com>, <carl@...amperecomputing.com>,
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Subject: Re: [PATCH v2 17/45] arm_mpam: resctrl: Pick the caches we will use
 as resctrl resources

On Fri, 19 Dec 2025 18:11:19 +0000
Ben Horgan <ben.horgan@....com> wrote:

> From: James Morse <james.morse@....com>
> 
> Systems with MPAM support may have a variety of control types at any point
> of their system layout. We can only expose certain types of control, and
> only if they exist at particular locations.
> 
> Start with the well-known caches. These have to be depth 2 or 3 and support
> MPAM's cache portion bitmap controls, with a number of portions fewer than
> resctrl's limit.
> 
> Signed-off-by: James Morse <james.morse@....com>
> Signed-off-by: Ben Horgan <ben.horgan@....com>
Reviewed-by: Jonathan Cameron <jonathan.cameron@...wei.com>

Note that I'm far from familiar with all the details of the resctl side
of things so assuming that will be well covered by other reviewers!

Jonathan

> ---
> Changes since rfc:
> Jonathan:
> Remove brackets
> Compress debug message
> Use temp var, r
> ---
>  drivers/resctrl/mpam_resctrl.c | 90 +++++++++++++++++++++++++++++++++-
>  1 file changed, 88 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/resctrl/mpam_resctrl.c b/drivers/resctrl/mpam_resctrl.c
> index 5481d9cc69d9..bc4f1c80eab5 100644
> --- a/drivers/resctrl/mpam_resctrl.c
> +++ b/drivers/resctrl/mpam_resctrl.c
> @@ -60,10 +60,95 @@ struct rdt_resource *resctrl_arch_get_resource(enum resctrl_res_level l)
>  	return &mpam_resctrl_controls[l].resctrl_res;
>  }
>  
> +static bool cache_has_usable_cpor(struct mpam_class *class)
> +{
> +	struct mpam_props *cprops = &class->props;
> +
> +	if (!mpam_has_feature(mpam_feat_cpor_part, cprops))
> +		return false;
> +
> +	/* resctrl uses u32 for all bitmap configurations */
> +	return class->props.cpbm_wd <= 32;
> +}