Peter Zijlstra <pet...@infradead.org> writes:
> 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().
It looks like it would only work for the first cpuid leaf, but we'll
need more than that. And the array makes it easier to allocate
attributes for sysfs en masse.
I guess it doesn't really matter if we use unions unless these bits need
to be exported to other parts of the kernel? But *that* is hardly a good
idea. What do you think?
Regards,
--
Alex
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