linux-kernel - Re: [PATCH 3/4] pwm: tegra: Add DT binding details to configure pin in suspends/resume

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Date:   Thu, 6 Apr 2017 15:03:54 +0100
From:   Jon Hunter <jonathanh@...dia.com>
To:     Laxman Dewangan <ldewangan@...dia.com>,
        Thierry Reding <thierry.reding@...il.com>
CC:     <robh+dt@...nel.org>, <mark.rutland@....com>,
        <linux-pwm@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-tegra@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        Linus Walleij <linus.walleij@...aro.org>
Subject: Re: [PATCH 3/4] pwm: tegra: Add DT binding details to configure pin
 in suspends/resume


On 06/04/17 14:19, Laxman Dewangan wrote:
> 
> On Thursday 06 April 2017 06:33 PM, Thierry Reding wrote:
>> * PGP Signed by an unknown key
>>
>> On Thu, Apr 06, 2017 at 09:57:09AM +0100, Jon Hunter wrote:
>>> On 05/04/17 15:13, Laxman Dewangan wrote:
>>>> +state of the system. The configuration of pin is provided via the
>>>> pinctrl
>>>> +DT node as detailed in the pinctrl DT binding document
>>>> +    Documentation/devicetree/bindings/pinctrl/pinctrl-bindings.txt
>>>> +
>>>> +The PWM node will have following optional properties.
>>>> +pinctrl-names:    Pin state names. Must be "suspend" and "resume".
>>> Why not just use the pre-defined names here? There is a pre-defined name
>>> for "default", "idle" and "sleep" and then you can use the following
>>> APIs and avoid the lookup of the state ...
>>>
>>> pinctrl_pm_select_default_state()
>>> pinctrl_pm_select_idle_state()
>>> pinctrl_pm_select_sleep_state()
>>>
>>> Note for i2c [0][1], I used "default" as the active/on state (which I
>>> know is not that descriptive) and then used 'idle' as the suspended
>>> state. This way we don't need any custom names.
>> Agreed, I think that's how these states are meant to be used.
> I did quick grep for the pinctrl_pm_select_* functions in the code tree
> and found usage of these APIs in some of the places.
> I am taking the reference of i2c-st, i2c-nomadic and
> extcon/extcon-usb-gpio.c drivers and from this the interpretation is
> 
> default state: When interface active and transfer need to be done in IO
> interface.
> idle state: Active state of the system but interface is not active, put
> in non-active state of the interface.
> sleep state: When system entering into suspend and IO interface is going
> to be inactive.
> 
> So in PWM case, we will need the "default" and "sleep" state.
> 
> In suspend(), set the "sleep" state and in resume, set the "default" state.
> 
> + Linus W as I refereed his st/nomadik driver for reference.

I mis-spoke before, I used 'idle' for i2c as I am using it in the
context of the runtime-pm callbacks and not suspend. So sleep is fine
with me.

Jon

-- 
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