linux-kernel - Re: [PATCH 9/9] clocksource: import ARC timer driver

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Date:   Thu, 3 Nov 2016 18:33:17 +0100
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Vineet Gupta <Vineet.Gupta1@...opsys.com>
Cc:     tglx@...utronix.de, linux-kernel@...r.kernel.org,
        linux-snps-arc@...ts.infradead.org,
        Noam Camus <noamca@...lanox.com>, Alexey.Brodkin@...opsys.com
Subject: Re: [PATCH 9/9] clocksource: import ARC timer driver

On Tue, Nov 01, 2016 at 01:57:05PM -0700, Vineet Gupta wrote:
> Hi Daniel,
> 
> On 11/01/2016 01:42 PM, Daniel Lezcano wrote:
> > Please stay consistent with the rest of the Kconfig.
> > 
> > config ARC_TIMER_RTC
> > 	bool "64-bit cycle counter in HS38 cores" if COMPILE_TEST
> > 	select CLKSRC_OF
> > 	help
> > 	  This counter provides 64-bit resolution vs. the 32-bit TIMER1.
> > 	  It is implemented inside the core thus can't be used in SMP systems.
> > 
> > config ARC_TIMER_GFRC
> > 	bool "64-bit cycle counter in ARConnect block in HS38x cores" if COMPILE_TEST
> > 	select CLKSRC_OF
> > 	help
> > 	  This counter can be used as clocksource in SMP HS38 SoCs.
> > 	  It sits outside the core thus can be used in SMP systems
> > 
> 
> Yes I did so already :-) Although I also added a default y if ARC to both, but as
> you say that is better done in ARC Kconfig.
> 
> > Then in the ARC's Kconfig you select ARC_TIMER_RTC or ARC_TIMER_GFRC depending
> > it is SMP or not.
> > 
> > One question:
> > 
> > Why ARC_TIMER_RTC can't be used in a SMP system ? Doesn't have each core its
> > own clocksource ? It seems you are assuming a clocksource can be used on SMP
> > only if the clocksource is unique and shared across the cores.
> 

As now the clksrc-probe is correctly handling the errors, if the rtc and the
gfrc are both defined in the DT, you can fail to init the rtc one with a simple
test in the init function:

	if (IS_DEFINED(CONFIG_SMP))
		return -EINVAL;

So, you can inconditionaly compile in both RTC and GFRC, no ? That would be
cleaner and prevent a different kernel config.