Re: [PATCH] MIPS: Add CPU option reporting to /proc/cpuinfo

[Hauke Mehrtens <hauke@hauke-m.de>]

On 12/27/18 2:08 PM, Kevin 'ldir' Darbyshire-Bryant wrote:
> 
> 
>> On 27 Dec 2018, at 12:39, Hauke Mehrtens <hauke@hauke-m.de> wrote:
>>
>>>
>> Hi Kevin,
>>
>> I do not see any condition based on CONFIG_MIPS_PERF_SHARED_TC_COUNTERS in arch/mips/include/asm/cpu-features.h, which kernel version did you use to test this patch? cpu_has_mipsmt_pertccounters was introduced between kernel 4.14 and 4.19, so it is not available in older kernel versions.
>>
>> Hauke
> 
> 
> This is 4.14.90 on openwrt…and I don’t think there are any sneaky backports involved in this area.
> 
> Take a look around line 131 of arch/mips/kernel/perf_event_mipsxx.c

Hi Kevin,

I assume you are talking about this:
https://elixir.bootlin.com/linux/v4.19.13/source/arch/mips/kernel/perf_event_mipsxx.c#L131

I still do not get why this is a problem.

If code wants to check if a feature is supported it includes 
"asm/cpu-features.h", this file then includes "cpu-feature-overrides.h".
For cpu-feature-overrides.h either the generic and empty version is 
provided or the SoC code has its own version with some SoC specific 
settings.

The asm/cpu-features.h file checks if the SoC code provided a special 
settings and if not it will add the code which will detect this feature 
dynamically, see here:
https://elixir.bootlin.com/linux/v4.19.13/source/arch/mips/include/asm/cpu-features.h#L577

This code should provide some settings independently of any Kconfig 
setting, for some Kconfig settings it is known that it is not active.

Hauke