[PATCH v2] arm64: perf: Add more support on caps under sysfs

[Will Deacon]

On Sat, May 29, 2021 at 02:19:46PM +0800, Shaokun Zhang wrote:
> Armv8.7 has introduced BUS_SLOTS and BUS_WIDTH in PMMIR_EL1 register,
> add two entries in caps for bus_slots and bus_width under sysfs. It
> will return the true slots and width if the information is available,
> otherwise it will return 0.
> 
> Cc: Will Deacon <will at kernel.org>
> Cc: Mark Rutland <mark.rutland at arm.com>
> Cc: Robin Murphy <robin.murphy at arm.com>
> Signed-off-by: Shaokun Zhang <zhangshaokun at hisilicon.com>
> ---
> ChangeLog:
> v1-->v2:
>     1. Address Robin's comment on bus_width calculation.
>     2. Add the comment on calculation formula.
> 
> Will & Robin,
> 
>     I don't change any about visible, if have more comments,
> please let me know.
> 
>  arch/arm64/include/asm/perf_event.h |  5 +++++
>  arch/arm64/kernel/perf_event.c      | 35 +++++++++++++++++++++++++++++++++++
>  2 files changed, 40 insertions(+)
> 
> diff --git a/arch/arm64/include/asm/perf_event.h b/arch/arm64/include/asm/perf_event.h
> index 60731f602d3e..4ef6f19331f9 100644
> --- a/arch/arm64/include/asm/perf_event.h
> +++ b/arch/arm64/include/asm/perf_event.h
> @@ -239,6 +239,11 @@
>  /* PMMIR_EL1.SLOTS mask */
>  #define ARMV8_PMU_SLOTS_MASK	0xff
>  
> +#define ARMV8_PMU_BUS_SLOTS_SHIFT 8
> +#define ARMV8_PMU_BUS_SLOTS_MASK 0xff
> +#define ARMV8_PMU_BUS_WIDTH_SHIFT 16
> +#define ARMV8_PMU_BUS_WIDTH_MASK 0xf
> +
>  #ifdef CONFIG_PERF_EVENTS
>  struct pt_regs;
>  extern unsigned long perf_instruction_pointer(struct pt_regs *regs);
> diff --git a/arch/arm64/kernel/perf_event.c b/arch/arm64/kernel/perf_event.c
> index f594957e29bd..453e0d8a442e 100644
> --- a/arch/arm64/kernel/perf_event.c
> +++ b/arch/arm64/kernel/perf_event.c
> @@ -317,8 +317,43 @@ static ssize_t slots_show(struct device *dev, struct device_attribute *attr,
>  
>  static DEVICE_ATTR_RO(slots);
>  
> +static ssize_t bus_slots_show(struct device *dev, struct device_attribute *attr,
> +			      char *page)
> +{
> +	struct pmu *pmu = dev_get_drvdata(dev);
> +	struct arm_pmu *cpu_pmu = container_of(pmu, struct arm_pmu, pmu);
> +	u32 bus_slots = (cpu_pmu->reg_pmmir >> ARMV8_PMU_BUS_SLOTS_SHIFT)
> +			& ARMV8_PMU_BUS_SLOTS_MASK;
> +
> +	return snprintf(page, PAGE_SIZE, "0x%08x\n", bus_slots);

Can you use sysfs_emit() instead?

> +}
> +
> +static DEVICE_ATTR_RO(bus_slots);
> +
> +static ssize_t bus_width_show(struct device *dev, struct device_attribute *attr,
> +			      char *page)
> +{
> +	struct pmu *pmu = dev_get_drvdata(dev);
> +	struct arm_pmu *cpu_pmu = container_of(pmu, struct arm_pmu, pmu);
> +	u32 bus_width = (cpu_pmu->reg_pmmir >> ARMV8_PMU_BUS_WIDTH_SHIFT)
> +			& ARMV8_PMU_BUS_WIDTH_MASK;
> +	u32 val;

Just initialise val to 0 here and drop the 'else' below.

> +	/* Encoded as Log2(number of bytes), plus one */
> +	if (bus_width > 2 && bus_width < 13)
> +		val = 1 << (bus_width - 1);
> +	else
> +		val = 0;
> +
> +	return snprintf(page, PAGE_SIZE, "0x%08x\n", val);

Again, sysfs_emit?

Will