[PATCH] perf/arm-cmn: Stop claiming entire iomem region

[Ilkka Koskinen]

Hi Robin,

On Thu, 19 Feb 2026, Robin Murphy wrote:
> So far, the PMU has been the only thing of interest in the vast mass
> of CMN registers, so we've gotten away with simply claiming the entire
> iomem region. However, now that we can support other features like MPAM
> controllers for the system caches, the PMU driver needs to stop being
> selfish and learn to share. Similarly to arm-ni, requesting just the
> DTC node(s) should suffice for staking our exclusive claim to the PMU
> features, as requesting hundreds of tiny regions for all the individual
> pmu_event_sel registers is definitely not worth the considerable bother.

Nice. It was on my list too but never really had time to work on. I was 
actually wondering whether we should claim all the PMU regions but I agree 
that would be a lot and pretty much pointless.

>
> As a consequence, we can also streamline the annoying CMN-600 special
> cases even more. The ACPI binding has in fact always specified a strict
> order for all resources, so we can reasonably drop the ancient pretence
> of swapping base and cfg, which IIRC was more just a moment of doubt on
> my part than anything else.
>
> Cc: James Morse <james.morse at arm.com>
> Signed-off-by: Robin Murphy <robin.murphy at arm.com>

Reviewed-by: Ilkka Koskinen <ilkka at os.amperecomputing.com>

Cheers, Ilkka


> ---
> drivers/perf/arm-cmn.c | 70 +++++++++++++++++++-----------------------
> 1 file changed, 31 insertions(+), 39 deletions(-)
>
> diff --git a/drivers/perf/arm-cmn.c b/drivers/perf/arm-cmn.c
> index 364a4fd8f2c0..6a5eba0be347 100644
> --- a/drivers/perf/arm-cmn.c
> +++ b/drivers/perf/arm-cmn.c
> @@ -2132,6 +2132,8 @@ static void arm_cmn_init_dtm(struct arm_cmn_dtm *dtm, struct arm_cmn_node *xp, i
> static int arm_cmn_init_dtc(struct arm_cmn *cmn, struct arm_cmn_node *dn, int idx)
> {
> 	struct arm_cmn_dtc *dtc = cmn->dtc + idx;
> +	const struct resource *cfg;
> +	resource_size_t base, size;
>
> 	dtc->pmu_base = dn->pmu_base;
> 	dtc->base = dtc->pmu_base - arm_cmn_pmu_offset(cmn, dn);
> @@ -2139,6 +2141,13 @@ static int arm_cmn_init_dtc(struct arm_cmn *cmn, struct arm_cmn_node *dn, int id
> 	if (dtc->irq < 0)
> 		return dtc->irq;
>
> +	cfg = platform_get_resource(to_platform_device(cmn->dev), IORESOURCE_MEM, 0);
> +	base = dtc->base - cmn->base + cfg->start;
> +	size = cmn->part == PART_CMN600 ? SZ_16K : SZ_64K;
> +	if (!devm_request_mem_region(cmn->dev, base, size, dev_name(cmn->dev)))
> +		return dev_err_probe(cmn->dev, -EBUSY,
> +				     "Failed to request DTC region 0x%llx\n", base);
> +
> 	writel_relaxed(CMN_DT_DTC_CTL_DT_EN, dtc->base + CMN_DT_DTC_CTL);
> 	writel_relaxed(CMN_DT_PMCR_PMU_EN | CMN_DT_PMCR_OVFL_INTR_EN, CMN_DT_PMCR(dtc));
> 	writeq_relaxed(0, CMN_DT_PMCCNTR(dtc));
> @@ -2525,43 +2534,26 @@ static int arm_cmn_discover(struct arm_cmn *cmn, unsigned int rgn_offset)
> 	return 0;
> }
>
> -static int arm_cmn600_acpi_probe(struct platform_device *pdev, struct arm_cmn *cmn)
> -{
> -	struct resource *cfg, *root;
> -
> -	cfg = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> -	if (!cfg)
> -		return -EINVAL;
> -
> -	root = platform_get_resource(pdev, IORESOURCE_MEM, 1);
> -	if (!root)
> -		return -EINVAL;
> -
> -	if (!resource_contains(cfg, root))
> -		swap(cfg, root);
> -	/*
> -	 * Note that devm_ioremap_resource() is dumb and won't let the platform
> -	 * device claim cfg when the ACPI companion device has already claimed
> -	 * root within it. But since they *are* already both claimed in the
> -	 * appropriate name, we don't really need to do it again here anyway.
> -	 */
> -	cmn->base = devm_ioremap(cmn->dev, cfg->start, resource_size(cfg));
> -	if (!cmn->base)
> -		return -ENOMEM;
> -
> -	return root->start - cfg->start;
> -}
> -
> -static int arm_cmn600_of_probe(struct device_node *np)
> +static int arm_cmn_get_root(struct arm_cmn *cmn, const struct resource *cfg)
> {
> +	const struct device_node *np = cmn->dev->of_node;
> +	const struct resource *root;
> 	u32 rootnode;
>
> -	return of_property_read_u32(np, "arm,root-node", &rootnode) ?: rootnode;
> +	if (cmn->part != PART_CMN600)
> +		return 0;
> +
> +	if (np)
> +		return of_property_read_u32(np, "arm,root-node", &rootnode) ?: rootnode;
> +
> +	root = platform_get_resource(to_platform_device(cmn->dev), IORESOURCE_MEM, 1);
> +	return root ? root->start - cfg->start : -EINVAL;
> }
>
> static int arm_cmn_probe(struct platform_device *pdev)
> {
> 	struct arm_cmn *cmn;
> +	const struct resource *cfg;
> 	const char *name;
> 	static atomic_t id;
> 	int err, rootnode, this_id;
> @@ -2575,16 +2567,16 @@ static int arm_cmn_probe(struct platform_device *pdev)
> 	cmn->cpu = cpumask_local_spread(0, dev_to_node(cmn->dev));
> 	platform_set_drvdata(pdev, cmn);
>
> -	if (cmn->part == PART_CMN600 && has_acpi_companion(cmn->dev)) {
> -		rootnode = arm_cmn600_acpi_probe(pdev, cmn);
> -	} else {
> -		rootnode = 0;
> -		cmn->base = devm_platform_ioremap_resource(pdev, 0);
> -		if (IS_ERR(cmn->base))
> -			return PTR_ERR(cmn->base);
> -		if (cmn->part == PART_CMN600)
> -			rootnode = arm_cmn600_of_probe(pdev->dev.of_node);
> -	}
> +	cfg = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> +	if (!cfg)
> +		return -EINVAL;
> +
> +	/* Map the whole region now, claim the DTCs once we've found them */
> +	cmn->base = devm_ioremap(cmn->dev, cfg->start, resource_size(cfg));
> +	if (IS_ERR(cmn->base))
> +		return PTR_ERR(cmn->base);
> +
> +	rootnode = arm_cmn_get_root(cmn, cfg);
> 	if (rootnode < 0)
> 		return rootnode;
>
> -- 
> 2.39.2.101.g768bb238c484.dirty
>
>