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Message-ID: <20141007110620.GG24725@leverpostej>
Date: Tue, 7 Oct 2014 12:06:20 +0100
From: Mark Rutland <mark.rutland@....com>
To: Sonny Rao <sonnyrao@...omium.org>
Cc: "linux-arm-kernel@...ts.infradead.org"
<linux-arm-kernel@...ts.infradead.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"dianders@...omium.org" <dianders@...omium.org>,
Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
Sudeep Holla <Sudeep.Holla@....com>,
Olof Johansson <olof@...om.net>,
Thomas Gleixner <tglx@...utronix.de>,
Daniel Lezcano <daniel.lezcano@...aro.org>,
Will Deacon <Will.Deacon@....com>,
Catalin Marinas <Catalin.Marinas@....com>,
Russell King <linux@....linux.org.uk>,
Stephen Boyd <sboyd@...eaurora.org>,
Marc Zyngier <Marc.Zyngier@....com>,
"stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: [PATCH v3] clocksource: arch_timer: Fix code to use physical
timers when requested
On Tue, Oct 07, 2014 at 05:34:16AM +0100, 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:
>
> * The firmware doesn't know and doesn't care about hypervisor mode and
> we don't want to add the complexity of hypervisor there.
>
> * The firmware isn't involved in SMP bringup or resume.
>
> * The ARCH timer come up with an uninitialized offset between the
> virtual and physical counters. Each core gets a different random
> offset.
>
> * The device boots in "Secure SVC" mode.
>
> * Nothing has touched the reset value of CNTHCTL.PL1PCEN or
> CNTHCTL.PL1PCTEN (both default to 1 at reset)
>
> One example of such as system is RK3288 where it is much simpler to
> use the physical counter since there's nobody managing the offset and
> each time a core goes down and comes back up it will get reinitialized
> to some other random value.
>
> Fixes: 0d651e4e65e9 ("clocksource: arch_timer: use virtual counters")
> Cc: stable@...r.kernel.org
> Signed-off-by: Sonny Rao <sonnyrao@...omium.org>
> Acked-by: Olof Johansson <olof@...om.net>
> ---
> v2: Add fixes tag to commit message, cc stable, copy Doug's
> description of the systems which need this in commit message.
> v3: Don't change the memory-mapped physical timer/counter code
> ---
> arch/arm/include/asm/arch_timer.h | 9 +++++++++
> arch/arm64/include/asm/arch_timer.h | 10 ++++++++++
> drivers/clocksource/arm_arch_timer.c | 25 ++++++++++++++++++++++---
> 3 files changed, 41 insertions(+), 3 deletions(-)
>
> diff --git a/arch/arm/include/asm/arch_timer.h b/arch/arm/include/asm/arch_timer.h
> index 0704e0c..e72aa4d 100644
> --- a/arch/arm/include/asm/arch_timer.h
> +++ b/arch/arm/include/asm/arch_timer.h
> @@ -78,6 +78,15 @@ static inline u32 arch_timer_get_cntfrq(void)
> return val;
> }
>
> +static inline u64 arch_counter_get_cntpct(void)
> +{
> + u64 cval;
> +
> + isb();
> + asm volatile("mrrc p15, 0, %Q0, %R0, c14" : "=r" (cval));
> + return cval;
> +}
> +
> static inline u64 arch_counter_get_cntvct(void)
> {
> u64 cval;
> diff --git a/arch/arm64/include/asm/arch_timer.h b/arch/arm64/include/asm/arch_timer.h
> index 9400596..58657c4 100644
> --- a/arch/arm64/include/asm/arch_timer.h
> +++ b/arch/arm64/include/asm/arch_timer.h
> @@ -135,6 +135,16 @@ static inline void arch_timer_evtstrm_enable(int divider)
> #endif
> }
>
> +static inline u64 arch_counter_get_cntpct(void)
> +{
> + u64 cval;
> +
> + isb();
> + asm volatile("mrs %0, cntpct_el0" : "=r" (cval));
> +
> + return cval;
> +}
> +
> static inline u64 arch_counter_get_cntvct(void)
> {
> u64 cval;
> diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
> index 5163ec1..bd8da15 100644
> --- a/drivers/clocksource/arm_arch_timer.c
> +++ b/drivers/clocksource/arm_arch_timer.c
> @@ -30,6 +30,8 @@
> #define CNTTIDR 0x08
> #define CNTTIDR_VIRT(n) (BIT(1) << ((n) * 4))
>
> +#define CNTPCT_LO 0x00
> +#define CNTPCT_HI 0x04
> #define CNTVCT_LO 0x08
> #define CNTVCT_HI 0x0c
> #define CNTFRQ 0x10
> @@ -386,6 +388,19 @@ static u64 arch_counter_get_cntvct_mem(void)
> return ((u64) vct_hi << 32) | vct_lo;
> }
>
> +static u64 arch_counter_get_cntpct_mem(void)
> +{
> + u32 pct_lo, pct_hi, tmp_hi;
> +
> + do {
> + pct_hi = readl_relaxed(arch_counter_base + CNTPCT_HI);
> + pct_lo = readl_relaxed(arch_counter_base + CNTPCT_LO);
> + tmp_hi = readl_relaxed(arch_counter_base + CNTPCT_HI);
> + } while (pct_hi != tmp_hi);
> +
> + return ((u64) pct_hi << 32) | pct_lo;
> +}
Theise MMIO timer changes should be dropped. They're unused below
anyhow.
Mark.
> +
> /*
> * Default to cp15 based access because arm64 uses this function for
> * sched_clock() before DT is probed and the cp15 method is guaranteed
> @@ -429,10 +444,14 @@ static void __init arch_counter_register(unsigned type)
> u64 start_count;
>
> /* Register the CP15 based counter if we have one */
> - if (type & ARCH_CP15_TIMER)
> - arch_timer_read_counter = arch_counter_get_cntvct;
> - else
> + if (type & ARCH_CP15_TIMER) {
> + if (arch_timer_use_virtual)
> + arch_timer_read_counter = arch_counter_get_cntvct;
> + else
> + arch_timer_read_counter = arch_counter_get_cntpct;
> + } else {
> arch_timer_read_counter = arch_counter_get_cntvct_mem;
> + }
>
> start_count = arch_timer_read_counter();
> clocksource_register_hz(&clocksource_counter, arch_timer_rate);
> --
> 1.8.3.2
>
>
--
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