On Tue, 2016-05-31 at 17:16 +1000, Oliver O'Halloran wrote:
> POWER ISA v3 adds large decrementer (LD) mode of operation which
> increases
> the size of the decrementer register from 32 bits to an implementation
> defined with of up to 64 bits.
> 
> This patch adds support for the LD on processors with the
> CPU_FTR_ARCH_300
> cpu feature flag set. For CPUs with this feature LD mode is enabled when
> when the ibm,dec-bits devicetree property is supplied for the boot CPU.
> The
> decrementer value is a signed quantity (with negative values indicating a
> pending exception) and this property is required to find the maximum
> positive decrementer value. If this property is not supplied then the
> traditional decrementer width of 32 bits is assumed and LD mode is
> disabled.
> 
> This patch was based on initial work by Jack Miller.
> 
> Signed-off-by: Oliver O'Halloran <ooh...@gmail.com>
> Cc: Michael Neuling <mi...@neuling.org>

Acked-by: Michael Neuling <mi...@neuling.org>

> Cc: Balbir Singh <bsinghar...@gmail.com>
> Cc: Jack Miller <j...@codezen.org>
> ---
>  arch/powerpc/include/asm/reg.h  |  1 +
>  arch/powerpc/include/asm/time.h |  6 +--
>  arch/powerpc/kernel/time.c      | 94
> +++++++++++++++++++++++++++++++++++++----
>  3 files changed, 90 insertions(+), 11 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/reg.h
> b/arch/powerpc/include/asm/reg.h
> index c1e82e968506..2793f3f03f9b 100644
> --- a/arch/powerpc/include/asm/reg.h
> +++ b/arch/powerpc/include/asm/reg.h
> @@ -332,6 +332,7 @@
>  #define   LPCR_AIL_0 0x00000000      /* MMU off exception
> offset 0x0 */
>  #define   LPCR_AIL_3 0x01800000      /* MMU on exception offset
> 0xc00...4xxx */
>  #define   LPCR_ONL   0x00040000      /* online - PURR/SPURR count
> */
> +#define   LPCR_LD    0x00020000      /* large decremeter */
>  #define   LPCR_PECE  0x0001f000      /* powersave exit cause
> enable */
>  #define     LPCR_PECEDP      0x00010000      /* directed priv dbells
> cause exit */
>  #define     LPCR_PECEDH      0x00008000      /* directed hyp dbells
> cause exit */
> diff --git a/arch/powerpc/include/asm/time.h
> b/arch/powerpc/include/asm/time.h
> index 1092fdd7e737..09211640a0e0 100644
> --- a/arch/powerpc/include/asm/time.h
> +++ b/arch/powerpc/include/asm/time.h
> @@ -146,7 +146,7 @@ static inline void set_tb(unsigned int upper,
> unsigned int lower)
>   * in auto-reload mode.  The problem is PIT stops counting when it
>   * hits zero.  If it would wrap, we could use it just like a
> decrementer.
>   */
> -static inline unsigned int get_dec(void)
> +static inline u64 get_dec(void)
>  {
>  #if defined(CONFIG_40x)
>       return (mfspr(SPRN_PIT));
> @@ -160,10 +160,10 @@ static inline unsigned int get_dec(void)
>   * in when the decrementer generates its interrupt: on the 1 to 0
>   * transition for Book E/4xx, but on the 0 to -1 transition for others.
>   */
> -static inline void set_dec(int val)
> +static inline void set_dec(u64 val)
>  {
>  #if defined(CONFIG_40x)
> -     mtspr(SPRN_PIT, val);
> +     mtspr(SPRN_PIT, (u32) val);
>  #else
>  #ifndef CONFIG_BOOKE
>       --val;
> diff --git a/arch/powerpc/kernel/time.c b/arch/powerpc/kernel/time.c
> index 3ed9a5a21d77..fe66f1c8d8b2 100644
> --- a/arch/powerpc/kernel/time.c
> +++ b/arch/powerpc/kernel/time.c
> @@ -96,7 +96,8 @@ static struct clocksource clocksource_timebase = {
>       .read         = timebase_read,
>  };
>  
> -#define DECREMENTER_MAX      0x7fffffff
> +#define DECREMENTER_DEFAULT_MAX 0x7FFFFFFF
> +u64 decrementer_max = DECREMENTER_DEFAULT_MAX;
>  
>  static int decrementer_set_next_event(unsigned long evt,
>                                     struct clock_event_device *dev);
> @@ -504,8 +505,8 @@ static void __timer_interrupt(void)
>               __this_cpu_inc(irq_stat.timer_irqs_event);
>       } else {
>               now = *next_tb - now;
> -             if (now <= DECREMENTER_MAX)
> -                     set_dec((int)now);
> +             if (now <= decrementer_max)
> +                     set_dec(now);
>               /* We may have raced with new irq work */
>               if (test_irq_work_pending())
>                       set_dec(1);
> @@ -535,7 +536,7 @@ void timer_interrupt(struct pt_regs * regs)
>       /* Ensure a positive value is written to the decrementer, or
> else
>        * some CPUs will continue to take decrementer exceptions.
>        */
> -     set_dec(DECREMENTER_MAX);
> +     set_dec(decrementer_max);
>  
>       /* Some implementations of hotplug will get timer interrupts
> while
>        * offline, just ignore these and we also need to set
> @@ -583,9 +584,9 @@ static void generic_suspend_disable_irqs(void)
>        * with suspending.
>        */
>  
> -     set_dec(DECREMENTER_MAX);
> +     set_dec(decrementer_max);
>       local_irq_disable();
> -     set_dec(DECREMENTER_MAX);
> +     set_dec(decrementer_max);
>  }
>  
>  static void generic_suspend_enable_irqs(void)
> @@ -866,7 +867,7 @@ static int decrementer_set_next_event(unsigned long
> evt,
>  
>  static int decrementer_shutdown(struct clock_event_device *dev)
>  {
> -     decrementer_set_next_event(DECREMENTER_MAX, dev);
> +     decrementer_set_next_event(decrementer_max, dev);
>       return 0;
>  }
>  
> @@ -892,6 +893,76 @@ static void register_decrementer_clockevent(int cpu)
>       clockevents_register_device(dec);
>  }
>  
> +static inline bool cpu_has_large_dec(void)
> +{
> +     return cpu_has_feature(CPU_FTR_ARCH_300);
> +}
> +
> +static inline bool large_dec_enabled(void)
> +{
> +     return (mfspr(SPRN_LPCR) & LPCR_LD) == LPCR_LD;
> +}
> +
> +/* enables the large decrementer for the current CPU */
> +static void enable_large_decrementer(void)
> +{
> +     /* do we have a large decrementer? */
> +     if (!cpu_has_large_dec())
> +             return;
> +
> +     /* do we need a large decrementer? */
> +     if (decrementer_max <= DECREMENTER_DEFAULT_MAX)
> +             return;
> +
> +     mtspr(SPRN_LPCR, mfspr(SPRN_LPCR) | LPCR_LD);
> +
> +     if (!large_dec_enabled()) {
> +             decrementer_max = DECREMENTER_DEFAULT_MAX;
> +
> +             pr_warn_once("time_init: Failed to enable large
> decrementer on CPU %d\n",
> +                     smp_processor_id());
> +     }
> +}
> +
> +static void __init set_decrementer_max(void)
> +{
> +     struct device_node *cpu;
> +     const __be32 *fp;
> +     u64 bits = 32;
> +
> +     cpu = of_find_node_by_type(NULL, "cpu");
> +     if (cpu)
> +             fp = of_get_property(cpu, "ibm,dec-bits", NULL);
> +
> +     if (cpu && fp) {
> +             u64 dt_bits = of_read_number(fp, 1);
> +
> +             bits = dt_bits;
> +             if (bits > 64)
> +                     bits = 64;
> +             else if (bits < 32)
> +                     bits = 32;
> +
> +             WARN(bits != dt_bits, "firmware supplied invalid
> ibm,dec-bits");
> +
> +             /*
> +              * Firmware says we support large dec but this cpu
> doesn't we
> +              * should warn about it. We can still limp along with
> default
> +              * 32 bit dec, but something is broken.
> +              */
> +             if (!cpu_has_large_dec()) {
> +                     WARN_ON(bits > 32);
> +                     bits = 32;
> +             }
> +
> +             /* calculate the signed maximum given this many bits */
> +             decrementer_max = (1ul << (bits - 1)) - 1;
> +     }
> +
> +     pr_info("time_init: %llu bit decrementer (max: %llx)\n",
> +             bits, decrementer_max);
> +}
> +
>  static void __init init_decrementer_clockevent(void)
>  {
>       int cpu = smp_processor_id();
> @@ -899,7 +970,7 @@ static void __init init_decrementer_clockevent(void)
>       clockevents_calc_mult_shift(&decrementer_clockevent,
> ppc_tb_freq, 4);
>  
>       decrementer_clockevent.max_delta_ns =
> -             clockevent_delta2ns(DECREMENTER_MAX,
> &decrementer_clockevent);
> +             clockevent_delta2ns(decrementer_max,
> &decrementer_clockevent);
>       decrementer_clockevent.min_delta_ns =
>               clockevent_delta2ns(2, &decrementer_clockevent);
>  
> @@ -908,6 +979,9 @@ static void __init init_decrementer_clockevent(void)
>  
>  void secondary_cpu_time_init(void)
>  {
> +     /* Enable the large decrementer (if we need to) */
> +     enable_large_decrementer();
> +
>       /* Start the decrementer on CPUs that have manual control
>        * such as BookE
>        */
> @@ -973,6 +1047,10 @@ void __init time_init(void)
>       vdso_data->tb_update_count = 0;
>       vdso_data->tb_ticks_per_sec = tb_ticks_per_sec;
>  
> +     /* initialise and enable the large decrementer (if we have one)
> */
> +     set_decrementer_max();
> +     enable_large_decrementer();
> +
>       /* Start the decrementer on CPUs that have manual control
>        * such as BookE
>        */
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