linux-kernel - Re: [PATCH v3 11/29] arm_mpam: Probe hardware to find the supported partid/pmg values

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Message-ID: <20251024184052.00004c24@huawei.com>
Date: Fri, 24 Oct 2025 18:40:52 +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>,
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Subject: Re: [PATCH v3 11/29] arm_mpam: Probe hardware to find the supported
 partid/pmg values

On Fri, 17 Oct 2025 18:56:27 +0000
James Morse <james.morse@....com> wrote:

> CPUs can generate traffic with a range of PARTID and PMG values,
> but each MSC may also have its own maximum size for these fields.
> Before MPAM can be used, the driver needs to probe each RIS on
> each MSC, to find the system-wide smallest value that can be used.
> The limits from requestors (e.g. CPUs) also need taking into account.
> 
> While doing this, RIS entries that firmware didn't describe are created
> under MPAM_CLASS_UNKNOWN.
> 
> While we're here, implement the mpam_register_requestor() call
> for the arch code to register the CPU limits. Future callers of this
> will tell us about the SMMU and ITS.
> 
> Signed-off-by: James Morse <james.morse@....com>
> Reviewed-by: Jonathan Cameron <jonathan.cameron@...wei.com>

Trivial stuff inline. I'd definitely not trust this reviewer who
is horribly inconsistent ;)

> Reviewed-by: Ben Horgan <ben.horgan@....com>
> Tested-by: Fenghua Yu <fenghuay@...dia.com>

>  static struct mpam_vmsc *
>  mpam_vmsc_alloc(struct mpam_component *comp, struct mpam_msc *msc)
>  {
> @@ -427,6 +500,7 @@ static int mpam_ris_create_locked(struct mpam_msc *msc, u8 ris_idx,
>  	cpumask_or(&comp->affinity, &comp->affinity, &ris->affinity);
>  	cpumask_or(&class->affinity, &class->affinity, &ris->affinity);
>  	list_add_rcu(&ris->vmsc_list, &vmsc->ris);
> +	list_add_rcu(&ris->msc_list, &msc->ris);

This looks like it might the add I was missing earlier?  If so and it can
only be done now, move the del into this patch as well.

>  
>  	return 0;
>  }
> @@ -446,9 +520,36 @@ int mpam_ris_create(struct mpam_msc *msc, u8 ris_idx,
>  	return err;
>  }
>  
> +static struct mpam_msc_ris *mpam_get_or_create_ris(struct mpam_msc *msc,
> +						   u8 ris_idx)
> +{
> +	int err;
> +	struct mpam_msc_ris *ris;
> +
> +	lockdep_assert_held(&mpam_list_lock);
> +
> +	if (!test_bit(ris_idx, &msc->ris_idxs)) {
> +		err = mpam_ris_create_locked(msc, ris_idx, MPAM_CLASS_UNKNOWN,
> +					     0, 0);
> +		if (err)
> +			return ERR_PTR(err);
> +	}
> +
> +	list_for_each_entry(ris, &msc->ris, msc_list) {
> +		if (ris->ris_idx == ris_idx) {
> +			return ris;

I'm not seeing this change in later patches in this series, so brackets
seem unnecessary and against kernel style.

> +		}
> +	}
> +
> +	return ERR_PTR(-ENOENT);
> +}
>