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: <50d2c651-746e-4ddd-4036-f72742a622f8@oss.nxp.com>
Date: Tue, 25 Mar 2025 15:21:13 +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>, NXP S32 Linux Team <s32@....com>
Subject: Re: [PATCH 2/2] clocksource/drivers/nxp-timer: Add the System Timer
 Module for the s32g platform

On 3/25/2025 2:51 PM, Daniel Lezcano wrote:
[ ... ]
>>>>>>> +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.
>>>
>>> The broadcast timer is stopped when it is unused which is the case for
>>> the s32 because there are no idle state powering down the local timers.
>>> They have to have be separated.
>>>
>>
>> This wouldn't be the case if the STM is kept running/counting during the
>> clock event setup, with only the clock event interrupt being disabled
>> (CCR.CEN).
> 
> Are you asking to use two different channels for the same STM instance,
> one for the clocksource and one for the clockevent ?
> 

I suggested using the CNT register to obtain the count for the clock
source, while using one of the STM channels for the clock event.

-- 
Regards,
Ghennadi