linux-kernel - Re: [PATCH 1/2] perf/arm-ni: rename PMU device name

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Message-ID: <aSR-Lu-nkSJl0V-x@willie-the-truck>
Date: Mon, 24 Nov 2025 15:47:58 +0000
From: Will Deacon <will@...nel.org>
To: Shouping Wang <allen.wang@...micro.com>
Cc: robin.murphy@....com, mark.rutland@....com,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	andy.xu@...micro.com, peter.du@...micro.com
Subject: Re: [PATCH 1/2] perf/arm-ni: rename PMU device name

On Fri, Nov 07, 2025 at 04:43:18PM +0800, Shouping Wang wrote:
> The PMU device names are arm_ni_1_*,arm_ni_2_*, etc. 
> The device names change based on the order of registration 
> for multiple NI instances. By naming the PMU device using 
> its address, the device name can be made independent of 
> the registration order.
> 
> Signed-off-by: Shouping Wang <allen.wang@...micro.com>
> ---
>  drivers/perf/arm-ni.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/perf/arm-ni.c b/drivers/perf/arm-ni.c
> index 1615a0564031..32eabdbe877a 100644
> --- a/drivers/perf/arm-ni.c
> +++ b/drivers/perf/arm-ni.c
> @@ -53,6 +53,7 @@
>  
>  #define NI_NUM_COUNTERS		8
>  #define NI_CCNT_IDX		31
> +#define NI_PMU_PA_SHIFT		12
>  
>  /* Event attributes */
>  #define NI_CONFIG_TYPE		GENMASK_ULL(15, 0)
> @@ -115,7 +116,6 @@ struct arm_ni {
>  	struct device *dev;
>  	void __iomem *base;
>  	enum ni_part part;
> -	int id;
>  	int cpu;
>  	int num_cds;
>  	struct hlist_node cpuhp_node;
> @@ -560,7 +560,7 @@ static int arm_ni_init_cd(struct arm_ni *ni, struct arm_ni_node *node, u64 res_s
>  		.read = arm_ni_event_read,
>  	};
>  
> -	name = devm_kasprintf(ni->dev, GFP_KERNEL, "arm_ni_%d_cd_%d", ni->id, cd->id);
> +	name = devm_kasprintf(ni->dev, GFP_KERNEL, "arm_ni_%llx", res_start >> NI_PMU_PA_SHIFT);

Doesn't this have the potential to break userspace (e.g. scripts) that
expect the current naming to be stable?

Either way, I'll need Robin's acks for these changes.

Will