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

[Shaokun Zhang]

Hi Will,

On 2021/6/3 0:42, Will Deacon wrote:
> 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?
> 

Ok,

>> +}
>> +
>> +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.
> 

Sure,

>> +	/* 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?

Got it and will fix these in next version.

Thanks,
Shaokun

> 
> Will
> .
>