linux-kernel - Re: [RFC 1/4] pwm: sifive: Add DT documentation for SiFive PWM Controller.

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Message-ID: <c702cf04-a565-dc76-a3bb-dbed922a9c80@wdc.com>
Date:   Tue, 16 Oct 2018 15:42:00 -0700
From:   Atish Patra <atish.patra@....com>
To:     Thierry Reding <thierry.reding@...il.com>
Cc:     Wesley Terpstra <wesley@...ive.com>, palmer@...ive.com,
        linux-riscv@...ts.infradead.org, linux-pwm@...r.kernel.org,
        linux-gpio@...r.kernel.org, linus.walleij@...aro.org,
        robh+dt@...nel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, mark.rutland@....com,
        hch@...radead.org
Subject: Re: [RFC 1/4] pwm: sifive: Add DT documentation for SiFive PWM
 Controller.

On 10/16/18 3:51 AM, Thierry Reding wrote:
> On Mon, Oct 15, 2018 at 03:45:46PM -0700, Atish Patra wrote:
>> On 10/10/18 6:51 AM, Thierry Reding wrote:
>>> On Tue, Oct 09, 2018 at 11:51:22AM -0700, Atish Patra wrote:
>>> [...]
>>>> +- interrupts: one interrupt per PWM channel (currently unused in the driver)
>>>
>>> This should probably say what the interrupt is used for. And once you
>>> have that, remove the comment about it being unused in the driver. DT
>>> is OS agnostic, so "driver" is very unspecific and your claim may
>>> actually be false.
>>>
>>> Thierry
>>>
>> As per my understanding, they are generated by hardware but no usage of pwm
>> interrupts as of now.
> 
> It might be useful to say when they are generated. Are they generated
> once per period? At the beginning or the end of the period? That kind
> of thing.
> 

Sure. I might have over simplified the statement above.
I could only find this about pwm interrupts in spec.
"The PWM can be configured to provide periodic counter interrupts by 
enabling auto-zeroing of the count register when a comparator 0 fires"

I may be wrong here but it looks like we need to configure the hardware 
to generate periodic interrupts. I will confirm with Wesly and update it 
in v2.

>> I am not sure if removing the entire entry is a good idea.
>> What would be the best way to represent that information ?
>>
>> May be this ?
>>
>> +-interrupts: one interrupt per PWM channel. No usage in HiFive Unleashed
>> SoC.
> 
> Why do you think you need to say that they are unused? If the hardware
> generates these interrupts, then they are "used". If no driver currently
> has a use for them, that's driver specific and doesn't belong in the DT
> bindings.
> 

Sounds good. I will update accordingly.

Regards,
Atish
> Thierry
>