Re: [RFCv4 1/7] drivers/perf: arm_pmu: add common attr group fields

[Will Deacon <will.deacon@arm.com>]

On Thu, Sep 08, 2016 at 11:21:46AM +0100, Mark Rutland wrote:
> In preparation for adding common attribute groups, add an array of
> attribute group pointers to arm_pmu, which will be used if the
> backend hasn't already set pmu::attr_groups.
> 
> Subsequent patches will move backends over to using these, before adding
> common fields.
> 
> Signed-off-by: Mark Rutland <mark.rutland@arm.com>
> Cc: Will Deacon <will.deacon@arm.com>
> ---
>  drivers/perf/arm_pmu.c       | 3 +++
>  include/linux/perf/arm_pmu.h | 9 ++++++++-
>  2 files changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/perf/arm_pmu.c b/drivers/perf/arm_pmu.c
> index f5e1008..145caf4 100644
> --- a/drivers/perf/arm_pmu.c
> +++ b/drivers/perf/arm_pmu.c
> @@ -1039,6 +1039,9 @@ int arm_pmu_device_probe(struct platform_device *pdev,
>  		goto out_free;
>  	}
>  
> +	if (!pmu->pmu.attr_groups)
> +		pmu->pmu.attr_groups = pmu->attr_groups;
> +
>  	ret = cpu_pmu_init(pmu);
>  	if (ret)
>  		goto out_free;
> diff --git a/include/linux/perf/arm_pmu.h b/include/linux/perf/arm_pmu.h
> index e188438..8030814 100644
> --- a/include/linux/perf/arm_pmu.h
> +++ b/include/linux/perf/arm_pmu.h
> @@ -14,7 +14,7 @@
>  
>  #include <linux/interrupt.h>
>  #include <linux/perf_event.h>
> -
> +#include <linux/sysfs.h>
>  #include <asm/cputype.h>
>  
>  /*
> @@ -77,6 +77,12 @@ struct pmu_hw_events {
>  	struct arm_pmu		*percpu_pmu;
>  };
>  
> +enum armpmu_attr_groups {
> +	ARMPMU_ATTR_GROUP_EVENTS,
> +	ARMPMU_ATTR_GROUP_FORMATS,
> +	ARMPMU_NR_ATTR_GROUPS
> +};
> +
>  struct arm_pmu {
>  	struct pmu	pmu;
>  	cpumask_t	active_irqs;
> @@ -111,6 +117,7 @@ struct arm_pmu {
>  	struct pmu_hw_events	__percpu *hw_events;
>  	struct list_head	entry;
>  	struct notifier_block	cpu_pm_nb;
> +	const struct attribute_group *attr_groups[ARMPMU_NR_ATTR_GROUPS + 1];

Is the '+ 1' because the array has to be NULL terminated? Probably worth
a comment to disuade people from sending "obvious" fixes.

Will