linux-kernel - Re: [PATCH v2 5/5] perf: arm_cspmu: ampere

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Date:   Thu, 1 Jun 2023 16:23:57 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Ilkka Koskinen <ilkka@...amperecomputing.com>,
        Jonathan Corbet <corbet@....net>,
        Will Deacon <will@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Besar Wicaksono <bwicaksono@...dia.com>,
        Suzuki K Poulose <suzuki.poulose@....com>
Cc:     linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 5/5] perf: arm_cspmu: ampere_cspmu: Add support for
 Ampere SoC PMU

On 2023-06-01 04:01, Ilkka Koskinen wrote:
[...]
> +static bool ampere_cspmu_validate_event(struct arm_cspmu *cspmu,
> +					struct perf_event *new)
> +{
> +	struct perf_event *curr;
> +	unsigned int idx;
> +	u32 threshold = 0, rank = 0, bank = 0;
> +
> +	/* We compare the global filter settings to existing events */
> +	idx = find_first_bit(cspmu->hw_events.used_ctrs,
> +			     cspmu->cycle_counter_logical_idx);
> +
> +	/* This is the first event */
> +	if (idx == cspmu->cycle_counter_logical_idx)
> +		return true;
> +
> +	curr = cspmu->hw_events.events[idx];
> +
> +	if (get_filter_enable(new)) {
> +		threshold	= get_threshold(new);
> +		rank		= get_rank(new);
> +		bank		= get_bank(new);
> +	}
> +
> +	if (get_filter_enable(new) != get_filter_enable(curr) ||

Is there any useful purpose in allowing the user to specify nonzero 
rank, bank or threshold values with filter_enable=0? Assuming not, then 
between this and ampere_cspmu_set_ev_filter() it appears that you don't 
need filter_enable at all.

Thanks,
Robin.

> +	    get_threshold(curr) != threshold ||
> +	    get_rank(curr) != rank ||
> +	    get_bank(curr) != bank)
> +		return false;
> +
> +	return true;
> +}