linux-kernel - Re: [PATCH v4 5/6] clocksource/drivers/exynos

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Message-ID: <fdf70587-5960-4420-b1a4-4fc2f467fd06@linaro.org>
Date: Wed, 25 Jun 2025 11:23:24 +0200
From: Daniel Lezcano <daniel.lezcano@...aro.org>
To: William McVicker <willmcvicker@...gle.com>
Cc: Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>,
 Thomas Gleixner <tglx@...utronix.de>, Krzysztof Kozlowski <krzk@...nel.org>,
 Alim Akhtar <alim.akhtar@...sung.com>, Rob Herring <robh@...nel.org>,
 Saravana Kannan <saravanak@...gle.com>, Donghoon Yu <hoony.yu@...sung.com>,
 Hosung Kim <hosung0.kim@...sung.com>, kernel-team@...roid.com,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
 John Stultz <jstultz@...gle.com>, Youngmin Nam <youngmin.nam@...sung.com>,
 Peter Griffin <peter.griffin@...aro.org>,
 Tudor Ambarus <tudor.ambarus@...aro.org>,
 André Draszik <andre.draszik@...aro.org>,
 Conor Dooley <conor+dt@...nel.org>, linux-samsung-soc@...r.kernel.org,
 devicetree@...r.kernel.org
Subject: Re: [PATCH v4 5/6] clocksource/drivers/exynos_mct: Add module support


Hi Will,

sorry I missed to add you in Cc but the following proposal help in the 
module conversion:

https://lore.kernel.org/all/20250625085715.889837-1-daniel.lezcano@linaro.org/


On 25/06/2025 01:47, William McVicker wrote:
> On 06/24/2025, Daniel Lezcano wrote:
>> On Fri, Jun 20, 2025 at 11:17:08AM -0700, Will McVicker wrote:
>>> From: Donghoon Yu <hoony.yu@...sung.com>
>>>
>>> On Arm64 platforms the Exynos MCT driver can be built as a module. On
>>> boot (and even after boot) the arch_timer is used as the clocksource and
>>> tick timer. Once the MCT driver is loaded, it can be used as the wakeup
>>> source for the arch_timer.
>>>
>>> Signed-off-by: Donghoon Yu <hoony.yu@...sung.com>
>>> Signed-off-by: Youngmin Nam <youngmin.nam@...sung.com>
>>> [original commit from https://android.googlesource.com/kernel/gs/+/8a52a8288ec7d88ff78f0b37480dbb0e9c65bbfd]
>>> Reviewed-by: Youngmin Nam <youngmin.nam@...sung.com>
>>> Tested-by: Youngmin Nam <youngmin.nam@...sung.com>
>>> Signed-off-by: Will McVicker <willmcvicker@...gle.com>
>>> ---
>>
>> ...
>>
>>> -static int __init mct_init_spi(struct device_node *np)
>>
>> __init_or_module
> 
> Thanks, I'll update in v5.
> 
>>
>>> +static int mct_init_spi(struct device_node *np)
>>>   {
>>>   	return mct_init_dt(np, MCT_INT_SPI);
>>>   }
>>>   
>>> -static int __init mct_init_ppi(struct device_node *np)
>>> +static int mct_init_ppi(struct device_node *np)
>>>   {
>>>   	return mct_init_dt(np, MCT_INT_PPI);
>>>   }
>>> -TIMER_OF_DECLARE(exynos4210, "samsung,exynos4210-mct", mct_init_spi);
>>> -TIMER_OF_DECLARE(exynos4412, "samsung,exynos4412-mct", mct_init_ppi);
>>
>> Are you sure this is not going to hurt the ARM platforms ? Here the
>> timer is enabled very early in the boot process while with this change
>> the timer will be available later.
> 
> I took a second look at the TIMER_OF_DECLARE() macro and FWICT the timer will
> only be enabled "very early" via timer_probe() if "MODULE" is not defined which
> is only defined when this specific driver is compiled as a module. Note, this
> "MODULE" define is not the same as the Kconfig option "CONFIG_MODULES".
> That is why in my v1 and v2 patch [1] I had:
> 
>   #ifdef MODULE
>     ...
>     module_platform_driver(exynos4_mct_driver);
>   #else
>     TIMER_OF_DECLARE(...)
>     TIMER_OF_DECLARE(...)
>   #endif
> 
> However, I dropped that since Saravana mentioned that we should not be using
> TIMER_OF_DECLARE() for drivers that can be modules. I don't have an ARM Exynos
> device to verify dropping TIMER_OF_DECLARE() is safe. So if you and Saravana
> agree, I can work on creating a patch to define TIMER_OF_DECLARE_MODULE() like
> you proposed in [2] to handle this for all the drivers that are used for both ARM and
> ARM64 SoCs.
> 
> Thanks,
> Will
> 
> [1] https://lore.kernel.org/all/6e6b0f5f-ac60-48bb-af6c-fa58658d2639@linaro.org/
> [2] https://lore.kernel.org/all/f2f914aa-c554-4135-afaa-f075537ed929@linaro.org/
> 
> <snip>


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