linux-kernel - Re: [PATCH 2/4] clocksource/drivers/arm_arch

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Message-ID: <52887b08-d5bc-4710-af7c-a70fab5e7f81@linaro.org>
Date: Thu, 14 Aug 2025 16:02:40 +0200
From: Daniel Lezcano <daniel.lezcano@...aro.org>
To: Marc Zyngier <maz@...nel.org>, Steven Price <steven.price@....com>
Cc: linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org,
 Lorenzo Pieralisi <lpieralisi@...nel.org>, Hanjun Guo
 <guohanjun@...wei.com>, Sudeep Holla <sudeep.holla@....com>,
 "Rafael J. Wysocki" <rafael@...nel.org>, Thomas Gleixner
 <tglx@...utronix.de>, Mark Rutland <mark.rutland@....com>
Subject: Re: [PATCH 2/4] clocksource/drivers/arm_arch_timer: Add standalone
 MMIO driver

On 14/08/2025 12:49, Marc Zyngier wrote:
> On Thu, 14 Aug 2025 11:13:47 +0100,
> Steven Price <steven.price@....com> wrote:
>>
>> On 07/08/2025 17:02, Marc Zyngier wrote:
>>> Add a new driver for the MMIO side of the ARM architected timer.
>>> Most of it has been lifted from the existing arch timer code,
>>> massaged, and finally rewritten.
>>>
>>> It supports both DT and ACPI as firmware descriptions.
>>>
>>> Signed-off-by: Marc Zyngier <maz@...nel.org>
>>> ---
>>>   MAINTAINERS                               |   1 +
>>>   drivers/clocksource/arm_arch_timer_mmio.c | 420 ++++++++++++++++++++++
>>>   2 files changed, 421 insertions(+)
>>>   create mode 100644 drivers/clocksource/arm_arch_timer_mmio.c
>>>
>> [...]
>>> +static void arch_timer_mmio_setup(struct arch_timer *at, int irq)
>>> +{
>>> +	at->evt = (struct clock_event_device) {
>>> +		.features		   = (CLOCK_EVT_FEAT_ONESHOT |
>>> +					      CLOCK_EVT_FEAT_DYNIRQ),
>>> +		.name			   = "arch_mem_timer",
>>> +		.rating			   = 400,
>>> +		.cpumask		   = cpu_possible_mask,
>>> +		.irq 			   = irq,
>>> +		.set_next_event		   = arch_timer_mmio_set_next_event,
>>> +		.set_state_oneshot_stopped = arch_timer_mmio_shutdown,
>>> +		.set_state_shutdown	   = arch_timer_mmio_shutdown,
>>> +	};
>>> +
>>> +	at->evt.set_state_shutdown(&at->evt);
>>> +
>>> +	clockevents_config_and_register(&at->evt, at->rate, 0xf, CLOCKSOURCE_MASK(56));
>>
>> This doesn't work on 32 bit - clockevents_config_and_register()'s final
>> argument is an unsigned long, and a 56 bit mask doesn't fit. This
>> triggers a compiler warning:
> 
> Already reported, see 20250814111657.7debc9f1@...b.auug.org.au.
> 
>> Possible this should really be min(CLOCKSOURCE_MASK(56), ULONG_MAX)? But
>> I'm not familiar enough with this code. Most likely it's dead code on a
>> 32 bit platform.
> 
> No, this definitely exists on 32bit crap, since it has been part of
> the architecture from the ARMv7+VE days.
> 
> I think this is more of an impedance mismatch between the
> CLOCKSOURCE_MASK() helper and the clockevents_config_and_register(),
> and a (unsigned long) cast would do the trick.
> 
> But it also means that the per-cpu timer also gets truncated the same
> way, and that has interesting impacts on how often the timer is
> reprogrammed.
> 
> Daniel, do you want a patch on top or a new series?

A new series please

Thanks


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