linux-kernel - Re: [PATCH] cpuidle/cpuidle-big_little: fix reading cpu id part number

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Date:	Fri, 8 Aug 2014 17:47:37 +0100
From:	Lorenzo Pieralisi <lorenzo.pieralisi@....com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Juri Lelli <Juri.Lelli@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Juri Lelli <juri.lelli@...il.com>
Subject: Re: [PATCH] cpuidle/cpuidle-big_little: fix reading cpu id part
 number

On Fri, Aug 08, 2014 at 02:21:05PM +0100, Russell King - ARM Linux wrote:
> On Fri, Aug 08, 2014 at 01:42:37PM +0100, Juri Lelli wrote:
> > Commit af040ffc9ba1 ("ARM: make it easier to check the CPU part number
> > correctly") changed ARM_CPU_PART_X masks, and the way they are returned and
> > checked against. Usage of read_cpuid_part_number() is now deprecated, and
> > calling places updated accordingly. This actually broke cpuidle-big_little
> > initialization, as bl_idle_driver_init() performs a check using and hardcoded
> > mask on cpu_id.
> > 
> > Update the check to reflect changes on ARM_CPU_PART_X masks. Also,
> > make the check easier to understand.
> 
> I don't like this "let's work out our own way to check the CPU type"
> stuff which people seem to create.  Let's try and do the job better
> and have some proper interfaces to do this kind of thing.
> 
> Maybe we should have smp_cpuid_part(cpu) which returns the CPU vendor/
> part identifier for the particular CPU in an efficient manner.

Ok, basically an inline function that either read and mask the cpuid
stashed at boot in cpu_data or read the part number straight away on UP.

Should it belong in asm/smp_plat.h ?

Thanks,
Lorenzo

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