[PATCH v3 1/2] powerpc/timer - large decrementer support
Michael Neuling
mikey at neuling.org
Tue May 31 16:25:36 AEST 2016
On Tue, 2016-05-10 at 14:57 +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 <oohall at gmail.com>
> Cc: Michael Neuling <mikey at neuling.org>
> Cc: Balbir Singh <bsingharora at gmail.com>
> Cc: Jack Miller <jack at codezen.org>
A couple or minor comments below.
I've tested this against v4.7-rc1 in the systemsim p9 model (not public
yet), with NO_HZ_FULL. From xmon I can see larger dec values being used
("Sr 16" in xmon).
If you fix the comments below I'm happy to ACK it.
Acked-by: Michael Neuling <mikey at neuling.org>
> ---
> arch/powerpc/include/asm/reg.h | 1 +
> arch/powerpc/include/asm/time.h | 6 +--
> arch/powerpc/kernel/time.c | 92 +++++++++++++++++++++++++++++++++++++----
> 3 files changed, 89 insertions(+), 10 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/reg.h b/arch/powerpc/include/asm/reg.h
> index f5f4c66bbbc9..ff581ed1ab9d 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 81b0900a39ee..0656e80cadbf 100644
> --- a/arch/powerpc/kernel/time.c
> +++ b/arch/powerpc/kernel/time.c
> @@ -95,7 +95,8 @@ 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);
> @@ -503,7 +504,7 @@ static void __timer_interrupt(void)
> __this_cpu_inc(irq_stat.timer_irqs_event);
> } else {
> now = *next_tb - now;
> - if (now <= DECREMENTER_MAX)
> + if (now <= decrementer_max)
> set_dec((int)now);
You can remove the int cast here now since set_dec() takes a u64.
> /* We may have raced with new irq work */
> if (test_irq_work_pending())
> @@ -534,7 +535,7 @@ 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
> @@ -582,9 +583,9 @@ 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)
> @@ -865,7 +866,7 @@ 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;
> }
>
> @@ -891,6 +892,76 @@ 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("time_init: Failed to enable large decrementer on CPU %d\n",
> + smp_processor_id());
Can you make this pr_warn_once() since every CPU is going to call this?
> + }
> +}
> +
> +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();
> @@ -898,7 +969,7 @@ 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);
>
> @@ -907,6 +978,9 @@ 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
> */
> @@ -972,6 +1046,10 @@ 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
> */
More information about the Linuxppc-dev
mailing list