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 17:29:02 +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 17:24, Krzysztof Kozlowski wrote:
>>>>> 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?)?
>> Cadence TTC IP can be used as timer(clocksource/clockevent) and PWM device.
>> We have drivers/clocksource/timer-cadence-ttc.c for clocksource/clockevent functionality. 
>> New driver for PWM functionality will be added to drivers/pwm/pwm-cadence.c (3/3 of this
>> Series).  In given SoC,  multiple instances of TTC IP are possible(ZynqMP  Ultrscale SoC has 4
>> Instances), few of them could be configured as clocksource/clockevent devices and others
>> as PWM ones. So,  cloksource as well as PWM drivers for cadence TTC IP would be enabled in 
>> the kernel. 
>>
>> Now in this scenario, each TTC device would be matching with 2 drivers, clocksource and PWM, since
>> compatible string is same.  If I don’t add #pwm-cells checking in clocksource driver and return 
>> -ENODEV based on that, each device would always bind with clocksource driver. PWM driver 
>> would never probe since clocksource driver probes ahead of PWM one in probing order.
> 
> None of these above explain why you need two drivers.

And please do not answer to this with again: "I have two drivers...".

> 
>>
>> I am exploring mfd to deal with said scenario. Do you see any better way to handle this? 
> 
> You basically repeated previous sentence about MFD without answering.
> Yeah, better way could be to have one driver. Why you cannot have it
> that way?
> 
> 
> Best regards,
> Krzysztof
> 

Best regards,
Krzysztof