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

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Date:   Fri, 7 Apr 2017 12:19:47 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Laxman Dewangan <ldewangan@...dia.com>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Jon Hunter <jonathanh@...dia.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        "linux-pwm@...r.kernel.org" <linux-pwm@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/4] pwm: tegra: Add DT binding details to configure pin
 in suspends/resume

On Thu, Apr 6, 2017 at 3:19 PM, Laxman Dewangan <ldewangan@...dia.com> wrote:
> On Thursday 06 April 2017 06:33 PM, Thierry Reding wrote:
>> 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.

It is actually documented:
include/linux/pinctrl/pinctrl-state.h

/*
 * Standard pin control state definitions
 */

/**
 * @PINCTRL_STATE_DEFAULT: the state the pinctrl handle shall be put
 *      into as default, usually this means the pins are up and ready to
 *      be used by the device driver. This state is commonly used by
 *      hogs to configure muxing and pins at boot, and also as a state
 *      to go into when returning from sleep and idle in
 *      .pm_runtime_resume() or ordinary .resume() for example.
 * @PINCTRL_STATE_INIT: normally the pinctrl will be set to "default"
 *      before the driver's probe() function is called.  There are some
 *      drivers where that is not appropriate becausing doing so would
 *      glitch the pins.  In those cases you can add an "init" pinctrl
 *      which is the state of the pins before drive probe.  After probe
 *      if the pins are still in "init" state they'll be moved to
 *      "default".
 * @PINCTRL_STATE_IDLE: the state the pinctrl handle shall be put into
 *      when the pins are idle. This is a state where the system is relaxed
 *      but not fully sleeping - some power may be on but clocks gated for
 *      example. Could typically be set from a pm_runtime_suspend() or
 *      pm_runtime_idle() operation.
 * @PINCTRL_STATE_SLEEP: the state the pinctrl handle shall be put into
 *      when the pins are sleeping. This is a state where the system is in
 *      its lowest sleep state. Could typically be set from an
 *      ordinary .suspend() function.
 */
#define PINCTRL_STATE_DEFAULT "default"
#define PINCTRL_STATE_INIT "init"
#define PINCTRL_STATE_IDLE "idle"
#define PINCTRL_STATE_SLEEP "sleep"

Yours,
Linus Walleij