linux-kernel - Re: [PATCH 1/4] intel_idle: stop using driver

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Date:	Sat, 02 Feb 2013 10:44:17 +0100
From:	Daniel Lezcano <daniel.lezcano@...aro.org>
To:	Len Brown <lenb@...nel.org>
CC:	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
	Lists Linaro-dev <linaro-dev@...ts.linaro.org>
Subject: Re: [PATCH 1/4] intel_idle: stop using driver_data for static flags

On 02/02/2013 03:16 AM, Len Brown wrote:
> 
>>> intel_idle already uses a driver-specific flag:
>>>
>>> #define CPUIDLE_FLAG_TLB_FLUSHED        0x10000
>>>
>>> This patch just uses 4 more bits along with that one.
>>
>> Ok. In this case it would make sense to move this flag out of the
>> generic core code to the intel_idle.c file ?
> 
> This flag is already local to intel_idle.c.
> If another architecture finds it useful,
> then yes, it would make sense to move it to the shared header.

Oh, right. Sorry I puzzled myself with the name. I was convinced it was
in the shared header.

>> and move the [dec/en]coding
>> macro flags_2_MWAIT_EAX and MWAIT_EAX_2_flags (with a more appropriate
>> name for a generic code) to the cpuidle.h file ?
> 
> I think that a driver's private flag definitions
> should remain local to the driver.  It makes no sense
> to pollute the name space of other drivers for stuff
> that doesn't mean anything to them.  MWAIT is pretty
> specific to x86 -- and re-naming it to something 'generic'
> isn't going to make the code easier to read.

Ok, let me rephrase it because I think how it was presented was not clear.

As we want to use the half of the state flags for private purpose, I
suggested to add the encoding/decoding function in the shared header file.

The mwait eax flags are not encoded and the CPUIDLE_FLAG_TLB_FLUSHED is
encoded.

I suggested to unify both and to use an encoding function from the
shared header file.

#define CPUIDLE_PRIVATE_FLAGS(_flags_) \
	((_flags_) << 16) & CPUIDLE_DRIVER_FLAGS_MASK

For example:

#define FLAG_TLB_FLUSHED CPUIDLE_PRIVATE_FLAGS(0x1)
#define FLAG_MWAIT_C1    CPUIDLE_PRIVATE_FLAGS(0x0)
#define FLAG_MWAIT_C2    CPUIDLE_PRIVATE_FLAGS(0x10)
#define FLAG_MWAIT_C3    CPUIDLE_PRIVATE_FLAGS(0x20)
#define FLAG_MWAIT_C4    CPUIDLE_PRIVATE_FLAGS(0x30)
#define FLAG_MWAIT_C5    CPUIDLE_PRIVATE_FLAGS(0x40)
#define FLAG_MWAIT_C6    CPUIDLE_PRIVATE_FLAGS(0x52)

And then:

...

.flags = FLAG_TLB_FLUSHED | FLAG_MWAIT_C2 | CPUIDLE_FLAG_TIME_VALID

...

But in the idle function, you need to retrieve the 'value' of the EAX
not a flag, so there is the need for an extra macro conversion and mask
the TLB flag.

Well, this is a detail, so feel free to ignore this suggestion :)

Thanks
  -- Daniel

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