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

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Date:   Thu, 3 Mar 2022 11:17:33 +0100
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     "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>
Cc:     "andriy.shevchenko@...ux.intel.com" 
        <andriy.shevchenko@...ux.intel.com>,
        "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 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

Thanks for the clarification

   -- D.



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