Re: [PATCH v5 12/20] x86: perf: intel_pt: Intel PT PMU driver

[Peter Zijlstra]

On Mon, Oct 13, 2014 at 04:45:40PM +0300, Alexander Shishkin wrote:
> +
> +enum cpuid_regs {
> +	CR_EAX = 0,
> +	CR_ECX,
> +	CR_EDX,
> +	CR_EBX
> +};
> +
> +/*
> + * Capabilities of Intel PT hardware, such as number of address bits or
> + * supported output schemes, are cached and exported to userspace as "caps"
> + * attribute group of pt pmu device
> + * (/sys/bus/event_source/devices/intel_pt/caps/) so that userspace can store
> + * relevant bits together with intel_pt traces.
> + */
> +#define PT_CAP(_n, _l, _r, _m)						\
> +	[PT_CAP_ ## _n] = { .name = __stringify(_n), .leaf = _l,	\
> +			    .reg = _r, .mask = _m }
> +
> +static struct pt_cap_desc {
> +	const char	*name;
> +	u32		leaf;
> +	u8		reg;
> +	u32		mask;
> +} pt_caps[] = {
> +	PT_CAP(max_subleaf,		0, CR_EAX, 0xffffffff),
> +	PT_CAP(cr3_filtering,		0, CR_EBX, BIT(0)),
> +	PT_CAP(topa_output,		0, CR_ECX, BIT(0)),
> +	PT_CAP(topa_multiple_entries,	0, CR_ECX, BIT(1)),
> +	PT_CAP(payloads_lip,		0, CR_ECX, BIT(31)),
> +};
> +
> +static u32 pt_cap_get(enum pt_capabilities cap)
> +{
> +	struct pt_cap_desc *cd = &pt_caps[cap];
> +	u32 c = pt_pmu.caps[cd->leaf * 4 + cd->reg];
> +	unsigned int shift = __ffs(cd->mask);
> +
> +	return (c & cd->mask) >> shift;
> +}

> +	if (test_cpu_cap(&boot_cpu_data, X86_FEATURE_INTEL_PT)) {
> +		for (i = 0; i < PT_CPUID_LEAVES; i++)
> +			cpuid_count(20, i,
> +				    &pt_pmu.caps[CR_EAX + i * 4],
> +				    &pt_pmu.caps[CR_EBX + i * 4],
> +				    &pt_pmu.caps[CR_ECX + i * 4],
> +				    &pt_pmu.caps[CR_EDX + i * 4]);
> +	} else
> +		return -ENODEV;

I would really rather you use bitfield unions for cpuid stuff, have a
look at union cpuid10_e[abd]x as used in
perf_event_intel.c:intel_pmu_init().
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