On Tue, Jul 28, 2015 at 9:11 AM, Krzysztof Kozlowski
<k.kozlow...@samsung.com> wrote:
> On 28.07.2015 06:28, Alexey Klimov wrote:
>> It was discovered that 64-bit mmio MCT counter holds
>> the same value as ARM arch timer 64-bit physical counter.
>> Even more: arch timer and MCT are same underlying hardware
>> timer.
>>
>> Patch adds code to MCT to allow it to read 64-bit counter
>> from coprocessor cp15 registers since it's way more
>> faster than reading the same counter from MCT mmio region.
>>
>> That functionality triggers only if special property
>> use-cp15-phys-counter is present in device tree,
>> only on 32-bit ARMv7 systems and only if HYP mode is
>> available.
>
> Hi,
>
> It would be nice to put here also the measurements from cover letter.
> This would be the justification for the commit.
Ok, I will add them. I will try to find time to perform more precise
measurements.
> I guess same optimization could be done for ARMv8 Exynos SoCs?
I honestly don't know, don't have access to ARMv8 Exynos SoCs.
If i remember correctly there are no public-available 64-bit Exynos
boards yet. Exynos7420 is on the way to be released.
The main concern is that MCT probably not enabled for arm64 and
some cleanup/re-factoring is required for cycles_t variable. See
message in exynos4_read_current_timer() in MCT.
Also ARMv8 requires arm generic timer to be available and fully
operational. So for me it looks like current upstream kernel will work
on top of arm arch timer.
>> Idea of rewriting accessors is taken from arm_arch_timer.c.
>>
>> By default MCT will read counter from mmio since it's
>> guaranteed to work.
>>
>> Signed-off-by: Alexey Klimov <klimov.li...@gmail.com>
>> ---
>> drivers/clocksource/exynos_mct.c | 77
>> ++++++++++++++++++++++++++++++++++------
>> 1 file changed, 67 insertions(+), 10 deletions(-)
>>
>> diff --git a/drivers/clocksource/exynos_mct.c
>> b/drivers/clocksource/exynos_mct.c
>> index 9064ff7..039b41c 100644
>> --- a/drivers/clocksource/exynos_mct.c
>> +++ b/drivers/clocksource/exynos_mct.c
>> @@ -26,6 +26,9 @@
>> #include <linux/clocksource.h>
>> #include <linux/sched_clock.h>
>>
>> +#include <asm/arch_timer.h> /* for cp15 physical arch timer counter */
>> +#include <asm/virt.h> /* for checking HYP mode */
>> +
>> #define EXYNOS4_MCTREG(x) (x)
>> #define EXYNOS4_MCT_G_CNT_L EXYNOS4_MCTREG(0x100)
>> #define EXYNOS4_MCT_G_CNT_U EXYNOS4_MCTREG(0x104)
>> @@ -82,6 +85,17 @@ static unsigned long clk_rate;
>> static unsigned int mct_int_type;
>> static int mct_irqs[MCT_NR_IRQS];
>>
>> +static u32 notrace __exynos4_read_count_32(void);
>> +static u64 __exynos4_read_count_64(void);
>> +
>> +/*
>> + * Default to __exynos4_read_count_{32,64} functions that reads counter from
>> + * MCT mmio region and this method is guaranteed
>> + * to exist (if MCT was successfully initialized).
>> + */
>> +u32 (*exynos4_read_count_32)(void) = __exynos4_read_count_32;
>> +u64 (*exynos4_read_count_64)(void) = __exynos4_read_count_64;
>
> I think these could be static.
Yeah. Will fix it right away.
>> +
>> struct mct_clock_event_device {
>> struct clock_event_device evt;
>> unsigned long base;
>> @@ -163,16 +177,16 @@ static void exynos4_mct_frc_start(void)
>> }
>>
>> /**
>> - * exynos4_read_count_64 - Read all 64-bits of the global counter
>> + * __exynos4_read_count_64 - Read all 64-bits of the global counter
>> *
>> - * This will read all 64-bits of the global counter taking care to make sure
>> - * that the upper and lower half match. Note that reading the MCT can be
>> quite
>> - * slow (hundreds of nanoseconds) so you should use the 32-bit (lower half
>> - * only) version when possible.
>> + * This will read all 64-bits of the global counter from MCT mmio region
>> + * taking care to make sure that the upper and lower half match.
>> + * Note that reading the MCT can be quite slow (hundreds of nanoseconds)
>> + * so you should use the 32-bit (lower half only) version when possible.
>> *
>> * Returns the number of cycles in the global counter.
>> */
>> -static u64 exynos4_read_count_64(void)
>> +static u64 __exynos4_read_count_64(void)
>> {
>> unsigned int lo, hi;
>> u32 hi2 = readl_relaxed(reg_base + EXYNOS4_MCT_G_CNT_U);
>> @@ -187,18 +201,45 @@ static u64 exynos4_read_count_64(void)
>> }
>>
>> /**
>> - * exynos4_read_count_32 - Read the lower 32-bits of the global counter
>> + * __exynos4_read_cp15_count_64 - Read all 64-bits of the global counter
>> + * from coprocessor regisers.
>> *
>> - * This will read just the lower 32-bits of the global counter. This is
>> marked
>> - * as notrace so it can be used by the scheduler clock.
>> + * Note that reading here is faster than reading from MCT mmio region.
>> + *
>> + * Returns the number of cycles in the global counter.
>> + */
>> +static u64 __exynos4_read_cp15_count_64(void)
>> +{
>> + return arch_counter_get_cntpct();
>> +}
>> +
>> +/**
>> + * __exynos4_read_count_32 - Read the lower 32-bits of the global counter
>> + *
>> + * This will read just the lower 32-bits of the global counter from
>> + * MCT mmio region.
>> + * This is marked as notrace so it can be used by the scheduler clock.
>> *
>> * Returns the number of cycles in the global counter (lower 32 bits).
>> */
>> -static u32 notrace exynos4_read_count_32(void)
>> +static u32 notrace __exynos4_read_count_32(void)
>> {
>> return readl_relaxed(reg_base + EXYNOS4_MCT_G_CNT_L);
>> }
>>
>> +/**
>> + * __exynos4_read_cp15_count_32 - Read the lower 32-bits of the global
>> counter
>> + *
>> + * This will read global counter from coprocessor regisers.
>
> s/regisers/registers/
Will fix it.
>> + * This is marked as notrace so it can be used by the scheduler clock.
>> + *
>> + * Returns the number of cycles in the global counter (lower 32 bits).
>> + */
>> +static u32 notrace __exynos4_read_cp15_count_32(void)
>> +{
>> + return arch_counter_get_cntpct();
>> +}
>> +
>> static cycle_t exynos4_frc_read(struct clocksource *cs)
>> {
>> return exynos4_read_count_32();
>> @@ -599,6 +640,22 @@ static void __init mct_init_dt(struct device_node *np,
>> unsigned int int_type)
>> for (i = MCT_L0_IRQ; i < nr_irqs; i++)
>> mct_irqs[i] = irq_of_parse_and_map(np, i);
>>
>> + /*
>> + * If use-cp15-phys-counter property is present in device tree
>> + * then use CP15 ARM arch timer 64-bit physical counter
>> + * to speedup reading since it keeps the same value like
>> + * 64-bit counter in MCT mmio region.
>> + * If HYP mode is available we can rely on physical
>> + * timer counter to be accessible from PL1.
>> + */
>> + if (IS_ENABLED(CONFIG_ARM) && is_hyp_mode_available() &&
>> + of_property_read_bool(np, "use-cp15-phys-counter")) {
>
> This looks like a property specific to Exynos. Add a "samsung," prefix.
>
> Best regards,
> Krzysztof
Agree.
Thanks for comments and review.
Best regards,
Alexey Klimov.
>> +
>> + /* point MCT functions to read counter from coprocessor */
>> + exynos4_read_count_32 = __exynos4_read_cp15_count_32;
>> + exynos4_read_count_64 = __exynos4_read_cp15_count_64;
>> + }
>> +
>> exynos4_timer_resources(np, of_iomap(np, 0));
>> exynos4_clocksource_init();
>> exynos4_clockevent_init();
>>
>
--
Best regards, Klimov Alexey
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