linux-kernel - Re: [LINUX PATCH v2 1/3] clocksource: timer-cadence-ttc: Do not probe TTC device configured as PWM

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Date:   Fri, 24 Nov 2023 12:35:44 +0100
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     "Sayyed, Mubin" <mubin.sayyed@....com>
Cc:     "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-pwm@...r.kernel.org" <linux-pwm@...r.kernel.org>,
        "git (AMD-Xilinx)" <git@....com>,
        "mubin10@...il.com" <mubin10@...il.com>,
        "krzysztof.kozlowski+dt@...aro.org" 
        <krzysztof.kozlowski+dt@...aro.org>,
        "u.kleine-koenig@...gutronix.de" <u.kleine-koenig@...gutronix.de>,
        "thierry.reding@...il.com" <thierry.reding@...il.com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "conor+dt@...nel.org" <conor+dt@...nel.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "daniel.lezcano@...aro.org" <daniel.lezcano@...aro.org>,
        "Simek, Michal" <michal.simek@....com>
Subject: Re: [LINUX PATCH v2 1/3] clocksource: timer-cadence-ttc: Do not probe
 TTC device configured as PWM

On 24/11/2023 12:03, Sayyed, Mubin wrote:
> Hi Krzysztof,
> 
>> -----Original Message-----
>> From: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
>> Sent: Wednesday, November 15, 2023 5:41 PM
>> To: Sayyed, Mubin <mubin.sayyed@....com>
>> Cc: linux-arm-kernel@...ts.infradead.org; linux-kernel@...r.kernel.org;
>> devicetree@...r.kernel.org; linux-pwm@...r.kernel.org; git (AMD-Xilinx)
>> <git@....com>; mubin10@...il.com; krzysztof.kozlowski+dt@...aro.org;
>> u.kleine-koenig@...gutronix.de; thierry.reding@...il.com;
>> robh+dt@...nel.org; conor+dt@...nel.org; tglx@...utronix.de;
>> daniel.lezcano@...aro.org; Simek, Michal <michal.simek@....com>
>> Subject: Re: [LINUX PATCH v2 1/3] clocksource: timer-cadence-ttc: Do not probe
>> TTC device configured as PWM
>>
>> On 15/11/2023 06:55, Sayyed, Mubin wrote:
>>>>> +	/*
>>>>> +	 * If pwm-cells property is present in TTC node,
>>>>> +	 * it would be treated as PWM device.
>>>>> +	 */
>>>>> +	if (of_property_read_bool(timer, "#pwm-cells"))
>>>>> +		return -ENODEV;
>>>>
>>>> You will introduce dmesg errors, so regressions.
>>>>
>>> [Mubin]: I will change it to "return 0" to avoid dmesg errors.
>>
>> No, because solution is wrong.
>>
>>>
>>>> This does not look right. What you want is to bind one device driver
>>>> and choose different functionality based on properties.
>>> [Mubin]:  I am doing it based on earlier discussion related to AXI Timer PWM
>> driver.  It was suggested to use #pwm-cells property for identifying role of
>> device(PWM/clocksource) https://lore.kernel.org/linux-
>> devicetree/20210513021631.GA878860@...h.at.kernel.org/.
>>
>> You are mixing bindings with driver. I said here about driver and yes - you must
>> use pwm-cells to differentiate that. It's obvious.
>>
>> So again, one driver binding.
> [Mubin]: I will explore whether mfd framework can be used to handle this.

You do not need MFD for this, because you do not have a really MFD. This
is just one device, so I expect here one driver. Why do you need
multiple drivers (which also would solve that problem but why?)?

Best regards,
Krzysztof