From: Daniel Lezcano <daniel.lezcano@linaro.org>
To: Chanwoo Choi <cw00.choi@samsung.com>,
Will Deacon <will@kernel.org>,
linux-kernel@vger.kernel.org
Cc: linux-arm-kernel@lists.infradead.org,
Marek Szyprowski <m.szyprowski@samsung.com>,
Krzysztof Kozlowski <krzk@kernel.org>,
Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>,
Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH 1/2] clocksource/drivers/exynos_mct: Prioritise Arm arch timer on arm64
Date: Wed, 16 Jun 2021 17:25:20 +0200 [thread overview]
Message-ID: <2a0181ea-a26e-65e9-16f6-cc233b6b296f@linaro.org> (raw)
In-Reply-To: <466bfc19-2260-87c6-c458-b43cf23617e3@samsung.com>
On 10/06/2021 03:03, Chanwoo Choi wrote:
> Hi,
>
> On 6/9/21 12:43 AM, Will Deacon wrote:
>> All arm64 CPUs feature an architected timer, which offers a relatively
>> low-latency interface to a per-cpu clocksource and timer. For the most
>> part, using this interface is a no-brainer, with the exception of SoCs
>> where it cannot be used to wake up from deep idle state (i.e.
>> CLOCK_EVT_FEAT_C3STOP is set).
>>
>> On the contrary, the Exynos MCT is extremely slow to access yet can be
>> used as a wakeup source. In preparation for using the Exynos MCT as a
>> potential wakeup timer for the Arm architected timer, reduce its ratings
>> so that the architected timer is preferred.
>>
>> This effectively reverts the decision made in 6282edb72bed
>> ("clocksource/drivers/exynos_mct: Increase priority over ARM arch timer")
>> for arm64, as the reasoning for the original change was to work around
>> a 32-bit SoC design.
>>
>> Cc: Marek Szyprowski <m.szyprowski@samsung.com>
>> Cc: Krzysztof Kozlowski <krzk@kernel.org>
>> Cc: Chanwoo Choi <cw00.choi@samsung.com>
>> Cc: Thomas Gleixner <tglx@linutronix.de>
>> Signed-off-by: Will Deacon <will@kernel.org>
>> ---
>> drivers/clocksource/exynos_mct.c | 13 +++++++++++--
>> 1 file changed, 11 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/clocksource/exynos_mct.c b/drivers/clocksource/exynos_mct.c
>> index fabad79baafc..804d3e01c8f4 100644
>> --- a/drivers/clocksource/exynos_mct.c
>> +++ b/drivers/clocksource/exynos_mct.c
>> @@ -51,6 +51,15 @@
>>
>> #define TICK_BASE_CNT 1
>>
>> +#ifdef CONFIG_ARM
>> +/* Use values higher than ARM arch timer. See 6282edb72bed. */
>> +#define MCT_CLKSOURCE_RATING 450
>> +#define MCT_CLKEVENTS_RATING 500
>> +#else
>> +#define MCT_CLKSOURCE_RATING 350
>> +#define MCT_CLKEVENTS_RATING 350
>> +#endif
>> +
>> enum {
>> MCT_INT_SPI,
>> MCT_INT_PPI
>> @@ -206,7 +215,7 @@ static void exynos4_frc_resume(struct clocksource *cs)
>>
>> static struct clocksource mct_frc = {
>> .name = "mct-frc",
>> - .rating = 450, /* use value higher than ARM arch timer */
>> + .rating = MCT_CLKSOURCE_RATING,
>> .read = exynos4_frc_read,
>> .mask = CLOCKSOURCE_MASK(32),
>> .flags = CLOCK_SOURCE_IS_CONTINUOUS,
>> @@ -457,7 +466,7 @@ static int exynos4_mct_starting_cpu(unsigned int cpu)
>> evt->set_state_oneshot_stopped = set_state_shutdown;
>> evt->tick_resume = set_state_shutdown;
>> evt->features = CLOCK_EVT_FEAT_PERIODIC | CLOCK_EVT_FEAT_ONESHOT;
>> - evt->rating = 500; /* use value higher than ARM arch timer */
>> + evt->rating = MCT_CLKEVENTS_RATING,
>>
>> exynos4_mct_write(TICK_BASE_CNT, mevt->base + MCT_L_TCNTB_OFFSET);
>>
>>
>
> I'm not sure that exynos mct is working without problem
> such as the case of 6282edb72bed.
> As described on On ,6282edb72bed the arch timer on exynos SoC
> depends on Exynos MCT device. the arch timer is not able to work
> without Exynos MCT because of using the common module.
Is it possible to change the DT to have a phandle to the exynos_mct, so
it will be probed before the arch_arm_timer ?
--
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next prev parent reply other threads:[~2021-06-16 15:25 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-08 15:43 [PATCH 0/2] Use Exynos-MCT timer as wakeup for Arm arch timer Will Deacon
2021-06-08 15:43 ` [PATCH 1/2] clocksource/drivers/exynos_mct: Prioritise Arm arch timer on arm64 Will Deacon
2021-06-09 11:41 ` Krzysztof Kozlowski
2021-06-10 1:03 ` Chanwoo Choi
2021-06-16 15:25 ` Daniel Lezcano [this message]
2021-06-17 0:58 ` Chanwoo Choi
2021-06-17 21:47 ` Will Deacon
2021-06-21 9:25 ` Daniel Lezcano
2021-06-21 10:10 ` Will Deacon
2021-06-21 10:18 ` Daniel Lezcano
2021-06-22 2:40 ` Chanwoo Choi
2021-06-22 5:21 ` Daniel Lezcano
2021-06-22 6:42 ` Chanwoo Choi
2021-06-21 10:17 ` Marek Szyprowski
2021-06-21 10:24 ` Daniel Lezcano
2021-08-26 16:25 ` [tip: timers/core] " tip-bot2 for Will Deacon
2021-06-08 15:43 ` [PATCH 2/2] clocksource/drivers/exynos_mct: Mark MCT device as CLOCK_EVT_FEAT_PERCPU Will Deacon
2021-06-09 11:41 ` Krzysztof Kozlowski
2021-06-17 0:59 ` Chanwoo Choi
2021-08-26 16:25 ` [tip: timers/core] " tip-bot2 for Will Deacon
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