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    Subject[PATCH 3.10 126/129] clocksource: arch_timer: use virtual counters
    Date
    3.10-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Mark Rutland <mark.rutland@arm.com>

    commit 0d651e4e65e96989f72236bf83bd4c6e55eb6ce4 upstream.

    Switching between reading the virtual or physical counters is
    problematic, as some core code wants a view of time before we're fully
    set up. Using a function pointer and switching the source after the
    first read can make time appear to go backwards, and having a check in
    the read function is an unfortunate block on what we want to be a fast
    path.

    Instead, this patch makes us always use the virtual counters. If we're a
    guest, or don't have hyp mode, we'll use the virtual timers, and as such
    don't care about CNTVOFF as long as it doesn't change in such a way as
    to make time appear to travel backwards. As the guest will use the
    virtual timers, a (potential) KVM host must use the physical timers
    (which can wake up the host even if they fire while a guest is
    executing), and hence a host must have CNTVOFF set to zero so as to have
    a consistent view of time between the physical timers and virtual
    counters.

    Signed-off-by: Mark Rutland <mark.rutland@arm.com>
    Acked-by: Catalin Marinas <catalin.marinas@arm.com>
    Acked-by: Marc Zyngier <marc.zyngier@arm.com>
    Acked-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
    Cc: Rob Herring <rob.herring@calxeda.com>
    Cc: Mark Brown <broonie@kernel.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    arch/arm/include/asm/arch_timer.h | 9 ---------
    arch/arm64/include/asm/arch_timer.h | 10 ----------
    drivers/clocksource/arm_arch_timer.c | 23 +++++------------------
    include/clocksource/arm_arch_timer.h | 2 +-
    4 files changed, 6 insertions(+), 38 deletions(-)

    --- a/arch/arm/include/asm/arch_timer.h
    +++ b/arch/arm/include/asm/arch_timer.h
    @@ -80,15 +80,6 @@ static inline u32 arch_timer_get_cntfrq(
    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;
    --- a/arch/arm64/include/asm/arch_timer.h
    +++ b/arch/arm64/include/asm/arch_timer.h
    @@ -110,16 +110,6 @@ static inline void __cpuinit arch_counte
    asm volatile("msr cntkctl_el1, %0" : : "r" (cntkctl));
    }

    -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;
    --- a/drivers/clocksource/arm_arch_timer.c
    +++ b/drivers/clocksource/arm_arch_timer.c
    @@ -186,27 +186,19 @@ u32 arch_timer_get_rate(void)
    return arch_timer_rate;
    }

    -/*
    - * Some external users of arch_timer_read_counter (e.g. sched_clock) may try to
    - * call it before it has been initialised. Rather than incur a performance
    - * penalty checking for initialisation, provide a default implementation that
    - * won't lead to time appearing to jump backwards.
    - */
    -static u64 arch_timer_read_zero(void)
    +u64 arch_timer_read_counter(void)
    {
    - return 0;
    + return arch_counter_get_cntvct();
    }

    -u64 (*arch_timer_read_counter)(void) = arch_timer_read_zero;
    -
    static cycle_t arch_counter_read(struct clocksource *cs)
    {
    - return arch_timer_read_counter();
    + return arch_counter_get_cntvct();
    }

    static cycle_t arch_counter_read_cc(const struct cyclecounter *cc)
    {
    - return arch_timer_read_counter();
    + return arch_counter_get_cntvct();
    }

    static struct clocksource clocksource_counter = {
    @@ -287,7 +279,7 @@ static int __init arch_timer_register(vo
    cyclecounter.mult = clocksource_counter.mult;
    cyclecounter.shift = clocksource_counter.shift;
    timecounter_init(&timecounter, &cyclecounter,
    - arch_counter_get_cntpct());
    + arch_counter_get_cntvct());

    if (arch_timer_use_virtual) {
    ppi = arch_timer_ppi[VIRT_PPI];
    @@ -376,11 +368,6 @@ static void __init arch_timer_init(struc
    }
    }

    - if (arch_timer_use_virtual)
    - arch_timer_read_counter = arch_counter_get_cntvct;
    - else
    - arch_timer_read_counter = arch_counter_get_cntpct;
    -
    arch_timer_register();
    arch_timer_arch_init();
    }
    --- a/include/clocksource/arm_arch_timer.h
    +++ b/include/clocksource/arm_arch_timer.h
    @@ -32,7 +32,7 @@
    #ifdef CONFIG_ARM_ARCH_TIMER

    extern u32 arch_timer_get_rate(void);
    -extern u64 (*arch_timer_read_counter)(void);
    +extern u64 arch_timer_read_counter(void);
    extern struct timecounter *arch_timer_get_timecounter(void);

    #else



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