linux-kernel - Re: [PATCH v8 2/2] clocksource: Add Intel Keem Bay timer support

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Date:   Thu, 3 Mar 2022 14:04:10 +0100
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     "andriy.shevchenko@...ux.intel.com" 
        <andriy.shevchenko@...ux.intel.com>
Cc:     "Sanil, Shruthi" <shruthi.sanil@...el.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "mgross@...ux.intel.com" <mgross@...ux.intel.com>,
        "Thokala, Srikanth" <srikanth.thokala@...el.com>,
        "Raja Subramanian, Lakshmi Bai" 
        <lakshmi.bai.raja.subramanian@...el.com>,
        "Sangannavar, Mallikarjunappa" 
        <mallikarjunappa.sangannavar@...el.com>
Subject: Re: [PATCH v8 2/2] clocksource: Add Intel Keem Bay timer support

On 03/03/2022 11:47, andriy.shevchenko@...ux.intel.com wrote:
> On Thu, Mar 03, 2022 at 11:17:33AM +0100, Daniel Lezcano wrote:
>> On 03/03/2022 07:18, Sanil, Shruthi wrote:
> 
>>>>>>>>> +	if (!(val & TIM_CONFIG_PRESCALER_ENABLE)) { +
>>>>>>>>> pr_err("%pOF: Prescaler is not enabled\n", np);
>>>>>>>>> +		ret = -ENODEV; +	}
>>>>>>>>
>>>>>>>> Why bail out instead of enabling the prescalar ?
>>>>>>>
>>>>>>> Because it is a secure register and it would be updated by
>>>>>>> the bootloader.
>>>>>> Should it be considered as a firmware bug ?
>>>>>
>>>>> No. This is a common driver across products in the series and
>>>>> enablement of this bit depends on the project requirements.
>>>>> Hence
>>>>> to be sure from driver, we added this check to avoid
>>>>> initialization of the driver in the case where it cannot be
>>>>> functional.
>>>>
>>>> I'm not sure to get the meaning of 'project requirements' but (for
>>>> my understanding) why not describe the timer in the DT for such
>>>> projects?
>>>>
>>>
>>> OK, I understand your point now. We can control the driver
>>> initialization from device tree binding rather than add a check in
>>> the driver. But isn't it good to have a check, if enabling of the bit
>>> is missed out in the FW? This can help in debugging.
>>
>> So if the description is in the DT but the prescaler bit is not enabled then
>> the firmware is buggy, IIUC. Yeah, this check would help, may be add more
>> context in the error message, eg. "Firmware has not enabled the prescaler
>> bit" or something like that
> 
> For this we also use a FW_BUG prefix to printf()-like functions.

Thanks for the information, I was unaware of this prefix.

Good to know ;)



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