[PATCHv4] powerpc/timer - large decrementer support
Denis Kirjanov
kirjanov at gmail.com
Thu Jun 23 18:02:01 AEST 2016
On 6/23/16, Oliver O'Halloran <oohall at gmail.com> wrote:
> Power ISAv3 adds a large decrementer (LD) mode which increases the size
> of the decrementer register. The size of the enlarged decrementer
> register is between 32 and 64 bits with the exact size being dependent
> on the implementation. When in LD mode, reads are sign extended to 64
> bits and a decrementer exception is raised when the high bit is set (i.e
> the value goes below zero). Writes however are truncated to the physical
> register width so some care needs to be taken to ensure that the high
> bit is not set when reloading the decrementer. This patch adds support
> for using the LD inside the host kernel on processors that support it.
>
> When LD mode is supported firmware will supply the ibm,dec-bits property
> for CPU nodes to allow the kernel to determine the maximum decrementer
> value. Enabling LD mode is a hypervisor privileged operation so the
> kernel can only enable it manually when running in hypervisor mode.
> Guest kernels that support LD mode can request it using the
> "ibm,client-architecture-support" firmware call or some other platform
> specific method. If this property is not supplied then the traditional
> decrementer width of 32 bit is assumed and LD mode will not be enabled.
>
> This patch was based on initial work by Jack Miller.
>
> Signed-off-by: Oliver O'Halloran <oohall at gmail.com>
> Signed-off-by: Balbir Singh <bsingharora at gmail.com>
> Cc: Michael Neuling <mikey at neuling.org>
> Cc: Jack Miller <jack at codezen.org>
> ---
> arch/powerpc/include/asm/reg.h | 1 +
> arch/powerpc/include/asm/time.h | 6 +--
> arch/powerpc/kernel/time.c | 102
> ++++++++++++++++++++++++++++++++++++----
> 3 files changed, 98 insertions(+), 11 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/reg.h b/arch/powerpc/include/asm/reg.h
> index a0948f40bc7b..12d970d64bb3 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 7a482a7f4d8d..aa6d399d939b 100644
> --- a/arch/powerpc/kernel/time.c
> +++ b/arch/powerpc/kernel/time.c
> @@ -97,7 +97,8 @@ 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);
> @@ -505,8 +506,8 @@ 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);
> @@ -536,7 +537,7 @@ 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
> @@ -584,9 +585,9 @@ 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)
> @@ -867,7 +868,7 @@ 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;
> }
>
> @@ -893,6 +894,84 @@ static void register_decrementer_clockevent(int cpu)
> clockevents_register_device(dec);
> }
>
> +static inline void check_large_decrementer(void)
> +{
> + u64 readback;
> +
> + mtspr(SPRN_DEC, decrementer_max);
> +
> + /*
> + * The decrementer's down counting will change the low bits. ORing with
> + * the default max ensure they are set.
> + */
> + readback = mfspr(SPRN_DEC) | DECREMENTER_DEFAULT_MAX;
> +
> + /*
> + * If we fail a readback test we need to reset decrementer_max to the
> + * 32 bit maximum. If the CPU has the LD disabled for whatever reason
> + * leaving it at a larger value would cause us to write into the high
> + * bit when handling decrementer exceptions, triggering another.
> + */
> +
> + pr_warn("time_init: readback got %llx, dec_max: %llx\n", readback,
> decrementer_max);
> +
> + if (readback != decrementer_max) {
> + decrementer_max = DECREMENTER_DEFAULT_MAX;
> +
> + pr_warn("time_init: large decrementer readback test failed on CPU %d,
> truncating to 32 bits\n",
> + smp_processor_id());
> + }
> +}
> +
> +static void enable_large_decrementer(void)
> +{
> + if (!cpu_has_feature(CPU_FTR_ARCH_300))
> + return;
> +
> + if (decrementer_max <= DECREMENTER_DEFAULT_MAX)
> + return;
> +
> + /*
> + * If we're running as the hypervisor we need to enable the LD manually
> + * otherwise firmware should have done it for us.
> + */
> + if (cpu_has_feature(CPU_FTR_HVMODE))
> + mtspr(SPRN_LPCR, mfspr(SPRN_LPCR) | LPCR_LD);
> +
> + check_large_decrementer();
> +}
> +
> +static void __init set_decrementer_max(void)
> +{
> + struct device_node *cpu;
> + const __be32 *fp;
> + u64 bits = 32;
> +
> + /* Prior to ISAv3 the decrementer is always 32 bit */
> + if (!cpu_has_feature(CPU_FTR_ARCH_300))
> + return;
> +
> + cpu = of_find_node_by_type(NULL, "cpu");
> + if (cpu)
> + fp = of_get_property(cpu, "ibm,dec-bits", NULL);
> +
> + if (cpu && fp) {
> + bits = of_read_number(fp, 1);
> +
> + if (bits > 64 || bits < 32) {
> + pr_warn("time_init: firmware supplied invalid ibm,dec-bits");
> + 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);
> +}
the call to of_node_put(cpu) is missing in the function.
> +
> static void __init init_decrementer_clockevent(void)
> {
> int cpu = smp_processor_id();
> @@ -900,7 +979,7 @@ 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);
>
> @@ -909,6 +988,9 @@ static void __init init_decrementer_clockevent(void)
>
> void secondary_cpu_time_init(void)
> {
> + /* Enable and test the large decrementer for this cpu */
> + enable_large_decrementer();
> +
> /* Start the decrementer on CPUs that have manual control
> * such as BookE
> */
> @@ -974,6 +1056,10 @@ 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
> */
> --
> 2.5.5
>
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--
Regards / Mit besten Grüßen,
Denis
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