linux-kernel - Re: [PATCH 2/2] clocksource/drivers/nxp-timer: Add the System Timer Module for the s32g platform

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Message-ID: <065d6f32-3161-8316-bbbd-4da18eef839b@oss.nxp.com>
Date: Tue, 25 Mar 2025 13:40:44 +0200
From: Ghennadi Procopciuc <ghennadi.procopciuc@....nxp.com>
To: Daniel Lezcano <daniel.lezcano@...aro.org>, tglx@...utronix.de
Cc: linux-kernel@...r.kernel.org, Thomas Fossati <thomas.fossati@...aro.org>,
 Larisa Grigore <Larisa.Grigore@....com>,
 Ghennadi Procopciuc <ghennadi.procopciuc@....com>,
 Maxime Coquelin <mcoquelin.stm32@...il.com>,
 Alexandre Torgue <alexandre.torgue@...s.st.com>,
 "moderated list:ARM/STM32 ARCHITECTURE"
 <linux-stm32@...md-mailman.stormreply.com>,
 "moderated list:ARM/STM32 ARCHITECTURE"
 <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 2/2] clocksource/drivers/nxp-timer: Add the System Timer
 Module for the s32g platform

On 3/25/2025 12:53 PM, Daniel Lezcano wrote:
[ ... ]
>>> +static int __init nxp_stm_clocksource_init(struct device *dev, const
>>> char *name,
>>> +                       void __iomem *base, struct clk *clk)
>>> +{
>>> +    struct stm_timer *stm_timer;
>>> +    int ret;
>>> +
>>> +    stm_timer = devm_kzalloc(dev, sizeof(*stm_timer), GFP_KERNEL);
>>> +    if (!stm_timer)
>>> +        return -ENOMEM;
>>> +
>>> +    stm_timer->base = base;
>>> +    stm_timer->rate = clk_get_rate(clk);
>>> +
>>> +    stm_timer->scs.cs.name = name;
>>> +    stm_timer->scs.cs.rating = 460;
>>> +    stm_timer->scs.cs.read = nxp_stm_clocksource_read;
>>> +    stm_timer->scs.cs.enable = nxp_stm_clocksource_enable;
>>> +    stm_timer->scs.cs.disable = nxp_stm_clocksource_disable;
>>> +    stm_timer->scs.cs.suspend = nxp_stm_clocksource_suspend;
>>> +    stm_timer->scs.cs.resume = nxp_stm_clocksource_resume;
>>> +    stm_timer->scs.cs.mask = CLOCKSOURCE_MASK(32);
>>> +    stm_timer->scs.cs.flags = CLOCK_SOURCE_IS_CONTINUOUS;
>>> +
>>> +    ret = clocksource_register_hz(&stm_timer->scs.cs, stm_timer->rate);
>>> +    if (ret)
>>> +        return ret;
>>
>> clocksource_unregister during remove callback for cleanup?
> 
> Sorry I don't get it :/
> 
> There is no cleanup after the clocksource_register_hz() is successful
> 

I noticed that other drivers, such as
drivers/clocksource/timer-tegra186.c and
drivers/clocksource/timer-sun5i.c, perform clocksource_unregister during
their platform_driver.remove callback. Shouldn't this apply here as well?

[ ... ]
> 
>>> +static int nxp_stm_clockevent_set_next_event(unsigned long delta,
>>> struct clock_event_device *ced)
>>> +{
>>> +    struct stm_timer *stm_timer = ced_to_stm(ced);
>>> +    u32 val;
>>> +
>>> +    nxp_stm_clockevent_disable(stm_timer);
>>
>> While examining the code base, I came across the
>> drivers/clocksource/timer-imx-gpt.c file, specifically the
>> mx1_2_set_next_event function, which includes a protection against
>> missing events. Using a similar approach would allow us to keep the STM
>> module enabled while only altering the channel's register state. This
>> risk can also be mitigated by adjusting min_delta_ns based on tick
>> frequency.
> 
> How would you validate that ?
> 

How would I validate that this works?

If this is the question, I see that the core performs an auto adjustment
of the minimum delta as part of the clockevents_program_min_delta
function when CONFIG_GENERIC_CLOCKEVENTS_MIN_ADJUST is enabled.
Initially, I would examine how many times dev->set_next_event() returns
-ETIME. At the end of the function, min_delta_ns should reflect the
actual minimum delta the device can handle.

[ ... ]
>>> +static int __init nxp_stm_timer_probe(struct platform_device *pdev)
>>> +{
>>> +    struct device *dev = &pdev->dev;
>>> +    struct device_node *np = dev->of_node;
>>> +    struct stm_instances *stm_instances;
>>> +    const char *name = of_node_full_name(np);
>>> +    void __iomem *base;
>>> +    int irq, ret;
>>> +    struct clk *clk;
>>> +
>>> +    stm_instances =
>>> (typeof(stm_instances))of_device_get_match_data(dev);
>>> +    if (!stm_instances) {
>>> +        dev_err(dev, "No STM instances associated with a cpu");
>>> +        return -EINVAL;
>>> +    }
>>> +
>>> +    base = devm_of_iomap(dev, np, 0, NULL);
>>> +    if (IS_ERR(base)) {
>>> +        dev_err(dev, "Failed to iomap %pOFn\n", np);
>>> +        return PTR_ERR(base);
>>> +    }
>>> +
>>> +    irq = irq_of_parse_and_map(np, 0);
>>> +    if (irq <= 0) {
>>> +        dev_err(dev, "Failed to parse and map IRQ: %d\n", irq);
>>> +        return -EINVAL;
>>> +    }
>>
>>  From commit description:
>>
>>> The first probed STM is used as a clocksource, the second will be the
>>> broadcast timer and the rest are used as a clockevent with the
>>> affinity set to a CPU.
>>
>> Why is the interrupt mandatory when the node is probed as a clocksource?
> 
> It relies on the DT description and it does not hurt to have a
> consistent code path for clockevent / clocksource even if the interrupt
> is not requested for the clocksource later.
> 

If so, in my opinion, it would make sense to use the same STM instance
for both the clocksource and broadcast clockevent, as both functions can
be accommodated within a single STM instance, which will help reduce the
number of STM instances used.

-- 
Regards,
Ghennadi