Re: [PATCH 1/2] clocksource/drivers/exynos_mct: Prioritise Arm arch timer on arm64

From: Daniel Lezcano <daniel.lezcano@linaro.org>
To: Will Deacon <will@kernel.org>, Chanwoo Choi <cw00.choi@samsung.com>
Cc: linux-kernel@vger.kernel.org,
	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: Mon, 21 Jun 2021 11:25:47 +0200	[thread overview]
Message-ID: <d79ebd58-1c4e-834c-fc06-482f25f6f3de@linaro.org> (raw)
In-Reply-To: <20210617214748.GC25403@willie-the-truck>

On 17/06/2021 23:47, Will Deacon wrote:
> On Thu, Jun 17, 2021 at 09:58:35AM +0900, Chanwoo Choi wrote:
>> On 6/17/21 12:25 AM, Daniel Lezcano wrote:
>>> On 10/06/2021 03:03, Chanwoo Choi wrote:
>>>> On 6/9/21 12:43 AM, Will Deacon wrote:
>>>>> 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 ?
>>
>> I think that DT changes is not proper way to keep the order between
>> exynos_mct and arch timer.
> 
> exynos4_mct_frc_start() is called unconditionally from probe via
> exynos4_clocksource_init() so as long as the mct probes first, then the
> arch timer should work, no? The rating shouldn't affect that.

How do you ensure the exynos mct is probed before the arch timer ?

The Makefile provides the right order, but the dependency is implicit.

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