linux-kernel - Re: [PATCH v5] clocksource: arch_timer: Fix code to use physical timers when requested

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Date:	Fri, 5 Dec 2014 18:41:04 +0800
From:	Yingjoe Chen <yingjoe.chen@...iatek.com>
To:	Sonny Rao <sonnyrao@...omium.org>
CC:	<linux-arm-kernel@...ts.infradead.org>,
	Mark Rutland <Mark.Rutland@....com>,
	Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
	Russell King <linux@....linux.org.uk>,
	Sudeep KarkadaNagesha <sudeep.karkadanagesha@....com>,
	Catalin Marinas <catalin.marinas@....com>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Will Deacon <will.deacon@....com>,
	<linux-kernel@...r.kernel.org>, <stable@...r.kernel.org>,
	<dianders@...omium.org>, Marc Zyngier <marc.zyngier@....com>,
	Sudeep Holla <Sudeep.Holla@....com>,
	Olof Johansson <olof@...om.net>,
	Thomas Gleixner <tglx@...utronix.de>,
	Stephen Boyd <sboyd@...eaurora.org>,
	Eddie Huang (黃智傑) 
	<eddie.huang@...iatek.com>
Subject: Re: [PATCH v5] clocksource: arch_timer: Fix code to use physical
 timers when requested

On Sun, 2014-11-23 at 23:02 -0800, Sonny Rao wrote: 
> This is a bug fix for using physical arch timers when
> the arch_timer_use_virtual boolean is false.  It restores the
> arch_counter_get_cntpct() function after removal in
> 
> 0d651e4e "clocksource: arch_timer: use virtual counters"
> 
> We need this on certain ARMv7 systems which are architected like this:
> diff --git a/arch/arm64/include/asm/arch_timer.h b/arch/arm64/include/asm/arch_timer.h
> index f190971..b1fa4e6 100644
> --- a/arch/arm64/include/asm/arch_timer.h
> +++ b/arch/arm64/include/asm/arch_timer.h
> @@ -104,6 +104,15 @@ static inline void arch_timer_set_cntkctl(u32 cntkctl)
>  	asm volatile("msr	cntkctl_el1, %0" : : "r" (cntkctl));
>  }
>  
> +static inline u64 arch_counter_get_cntpct(void)
> +{
> +	/*
> +	 * AArch64 kernel and user space mandate the use of CNTVCT.
> +	 */
> +	BUG();
> +	return 0;
> +}
> +
>  static inline u64 arch_counter_get_cntvct(void)
>  {
>  	u64 cval;

I tested this on an arm64 platform and system fail to boot when apply
this patch.

The boot loader start kernel at EL2, so is_hyp_mode_available() will be
true and we will use physical timer. Without this patch,
arch_timer_read_counter set to arch_counter_get_cntvct even when we use
physical timer which is incorrect but at least system will boot.

I think we still need this function on arm64. We should add BUG() to
arch_timer_init instead, maybe something like this:


@@ -708,9 +708,12 @@ static void __init arch_timer_init(struct device_node *np)
 	 * If we cannot rely on firmware initializing the timer registers then
 	 * we should use the physical timers instead.
 	 */
-	if (IS_ENABLED(CONFIG_ARM) &&
-	    of_property_read_bool(np, "arm,cpu-registers-not-fw-configured"))
+	if (of_property_read_bool(np, "arm,cpu-registers-not-fw-configured")) {
+		if (IS_ENABLED(CONFIG_ARM64))
+			BUG();
+		else
 			arch_timer_use_virtual = false;
+	}

Joe.C


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