Subject: [PATCH 1/2] ARM: arch timer: implement read_current_timer and get_cycles

From: [email-masked] (Stephen Boyd)
Date: Mon, 25 Jun 2012 14:39:04 -0700

On 06/22/12 08:09, Will Deacon wrote:
> This patch implements read_current_timer using the architected timers
> when they are selected via CONFIG_ARM_ARCH_TIMER. If they are detected
> not to be usable at runtime, we return -ENXIO to the caller.
>
> Furthermore, if read_current_timer is exported then we can implement
> get_cycles in terms of it for use as both an entropy source and for
> implementing __udelay and friends.

Neat.

> diff --git a/arch/arm/include/asm/timex.h b/arch/arm/include/asm/timex.h
> index 3be8de3..ce11944 100644
> --- a/arch/arm/include/asm/timex.h
> +++ b/arch/arm/include/asm/timex.h
> @@ -12,13 +12,15 @@
>  #ifndef _ASMARM_TIMEX_H
>  #define _ASMARM_TIMEX_H
>  
> +#include <asm/arch_timer.h>

This seems to cause compilation failures if you aren't building with
architected timers enabled.

In file included from arch/arm/include/asm/timex.h:15,
                 from include/linux/timex.h:174,
                 from include/linux/sched.h:57,
                 from arch/arm/kernel/asm-offsets.c:13:
arch/arm/include/asm/arch_timer.h: In function 'arch_timer_of_register':
arch/arm/include/asm/arch_timer.h:11: error: 'ENXIO' undeclared (first use in this function)

>  #include <mach/timex.h>
>  
>  typedef unsigned long cycles_t;
>  
> -static inline cycles_t get_cycles (void)
> -{
> -	return 0;
> -}
> +#ifdef ARCH_HAS_READ_CURRENT_TIMER
> +#define get_cycles()	({ cycles_t c; read_current_timer(&c) ? 0 : c; })
> +#else
> +#define get_cycles()	(0)
> +#endif
>  
>  #endif
> diff --git a/arch/arm/kernel/arch_timer.c b/arch/arm/kernel/arch_timer.c
> index dd58035..dbbeec4 100644
> --- a/arch/arm/kernel/arch_timer.c
> +++ b/arch/arm/kernel/arch_timer.c
> @@ -223,6 +223,14 @@ static cycle_t arch_counter_read(struct clocksource *cs)
>  	return arch_counter_get_cntpct();
>  }
>  
> +int read_current_timer(unsigned long *timer_val)
> +{
> +	if (!arch_timer_rate)
> +		return -ENXIO;

Shouldn't this be returning 0? Otherwise get_cycles() up there will
evaluate to -ENXIO?

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