[PATCH v1 1/1] gpio: of: provide option generic property for initial line states

[PATCH v1 1/1] gpio: of: provide option generic property for initial line states

[Oleksij Rempel]

This property is needed for barebox or may be other bootloaders
to set proper gpio configuration as early as possible.

This example is mainly based on "lines-initial-states" property
from this binding documentation:
Documentation/devicetree/bindings/gpio/gpio-pcf857x.txt

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
---
 Documentation/devicetree/bindings/gpio/gpio.txt | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/Documentation/devicetree/bindings/gpio/gpio.txt b/Documentation/devicetree/bindings/gpio/gpio.txt
index 84ede036f73d..60f8e8d8ab32 100644
--- a/Documentation/devicetree/bindings/gpio/gpio.txt
+++ b/Documentation/devicetree/bindings/gpio/gpio.txt
@@ -181,6 +181,26 @@ gpio-controller@00000000 {
 		"poweroff", "reset";
 }
 
+Optionally, a GPIO controller may have a "gpio-lines-initial-states" property.
+This is an array of values that specifies the initial state of each line. When
+a value is set to one, the corresponding line will be initialized to the input
+(pulled-up) state. When the values is set to two, the line will be initialized
+the low-level output state. If values is set to zero the line will be
+initialized to the input state.
+If the property is not specified no specific configuration will be set. Driver
+should reuse HW configuration provided by bootloader or other system.
+
+Example:
+
+gpio-controller@00000000 {
+	compatible = "foo";
+	reg = <0x00000000 0x1000>;
+	gpio-controller;
+	#gpio-cells = <2>;
+	ngpios = <9>;
+	gpio-lines-initial-states = <0>, <1>, <2>, <0>, <0>, <2>, <2>, <1>, <1>;
+}
+
 The GPIO chip may contain GPIO hog definitions. GPIO hogging is a mechanism
 providing automatic GPIO request and configuration as part of the
 gpio-controller's driver probe function.
-- 
2.11.0

Re: [PATCH v1 1/1] gpio: of: provide option generic property for initial line states

[Rob Herring]

On Fri, Jun 9, 2017 at 9:16 AM, Oleksij Rempel <o.rempel-bIcnvbaLZ9MEGnE8C9+IrQ@public.gmane.org> wrote:
> This property is needed for barebox or may be other bootloaders
> to set proper gpio configuration as early as possible.
>
> This example is mainly based on "lines-initial-states" property
> from this binding documentation:
> Documentation/devicetree/bindings/gpio/gpio-pcf857x.txt

Don't we have a binding for this already based on gpio-hogs.

Rob
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Re: [PATCH v1 1/1] gpio: of: provide option generic property for initial line states

[Oleksij Rempel]

Hi Rob,

On Fri, Jun 09, 2017 at 10:41:30AM -0500, Rob Herring wrote:
> On Fri, Jun 9, 2017 at 9:16 AM, Oleksij Rempel <o.rempel@pengutronix.de> wrote:
> > This property is needed for barebox or may be other bootloaders
> > to set proper gpio configuration as early as possible.
> >
> > This example is mainly based on "lines-initial-states" property
> > from this binding documentation:
> > Documentation/devicetree/bindings/gpio/gpio-pcf857x.txt
> 
> Don't we have a binding for this already based on gpio-hogs.

Markus Pargmann was working on this topic before and suddenly was not
able to finish it.
I found only some not finished discussions and no code or documentation
in linux kernel upstream.

So far, I was able to find fallowing patches and discussions:
patch 23.08.2015, last comment 11.05.2017:
https://patchwork.kernel.org/patch/7096721/

patch 23.02.2016, last comment 09.03.2016:
https://patchwork.ozlabs.org/patch/586743/

Since there was objections about node-like design for gpio-initval, I
provided an array property, which is similar to initval properties already used
for different other device nodes. For example:

Documentation/devicetree/bindings/net/wireless/qcom,ath10k.txt
qcom,ath10k-calibration-data

Documentation/devicetree/bindings/gpio/gpio-pcf857x.txt
lines-initial-states

Please fixme if I miss something.

-- 
Pengutronix e.K.                           |                             |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |
Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0    |
Amtsgericht Hildesheim, HRA 2686           | Fax:   +49-5121-206917-5555 |

Re: [PATCH v1 1/1] gpio: of: provide option generic property for initial line states

[Vladimir Zapolskiy]

Hi Oleksij,

On 06/11/2017 09:19 AM, Oleksij Rempel wrote:
> Hi Rob,
> 
> On Fri, Jun 09, 2017 at 10:41:30AM -0500, Rob Herring wrote:
>> On Fri, Jun 9, 2017 at 9:16 AM, Oleksij Rempel <o.rempel@pengutronix.de> wrote:
>>> This property is needed for barebox or may be other bootloaders
>>> to set proper gpio configuration as early as possible.
>>>
>>> This example is mainly based on "lines-initial-states" property
>>> from this binding documentation:
>>> Documentation/devicetree/bindings/gpio/gpio-pcf857x.txt
>>
>> Don't we have a binding for this already based on gpio-hogs.
> 
> Markus Pargmann was working on this topic before and suddenly was not
> able to finish it.

that's fine, but the proposed extension is supposedly not wanted.

> I found only some not finished discussions and no code or documentation
> in linux kernel upstream.
> 
> So far, I was able to find fallowing patches and discussions:
> patch 23.08.2015, last comment 11.05.2017:
> https://patchwork.kernel.org/patch/7096721/
> 
> patch 23.02.2016, last comment 09.03.2016:
> https://patchwork.ozlabs.org/patch/586743/
> 
> Since there was objections about node-like design for gpio-initval, I
> provided an array property, which is similar to initval properties already used
> for different other device nodes. For example:
> 
> Documentation/devicetree/bindings/net/wireless/qcom,ath10k.txt
> qcom,ath10k-calibration-data
> 
> Documentation/devicetree/bindings/gpio/gpio-pcf857x.txt
> lines-initial-states

It'd rather be better to fix the drivers and remove the properties
from these found device tree binding descriptions.

> 
> Please fixme if I miss something.

Why is GPIO hogging mechanism not good enough for your purpose?

--
With best wishes,
Vladimir

Re: [PATCH v1 1/1] gpio: of: provide option generic property for initial line states

[Oleksij Rempel]

Hi Vladimir,

On Sun, Jun 11, 2017 at 10:57:18PM +0300, Vladimir Zapolskiy wrote:
> Hi Oleksij,
> 
> On 06/11/2017 09:19 AM, Oleksij Rempel wrote:
> > Hi Rob,
> > 
> > On Fri, Jun 09, 2017 at 10:41:30AM -0500, Rob Herring wrote:
> >> On Fri, Jun 9, 2017 at 9:16 AM, Oleksij Rempel <o.rempel@pengutronix.de> wrote:
> >>> This property is needed for barebox or may be other bootloaders
> >>> to set proper gpio configuration as early as possible.
> >>>
> >>> This example is mainly based on "lines-initial-states" property
> >>> from this binding documentation:
> >>> Documentation/devicetree/bindings/gpio/gpio-pcf857x.txt
> >>
> >> Don't we have a binding for this already based on gpio-hogs.
> > 
> > Markus Pargmann was working on this topic before and suddenly was not
> > able to finish it.
> 
> that's fine, but the proposed extension is supposedly not wanted.

:(

> > I found only some not finished discussions and no code or documentation
> > in linux kernel upstream.
> > 
> > So far, I was able to find fallowing patches and discussions:
> > patch 23.08.2015, last comment 11.05.2017:
> > https://patchwork.kernel.org/patch/7096721/
> > 
> > patch 23.02.2016, last comment 09.03.2016:
> > https://patchwork.ozlabs.org/patch/586743/
> > 
> > Since there was objections about node-like design for gpio-initval, I
> > provided an array property, which is similar to initval properties already used
> > for different other device nodes. For example:
> > 
> > Documentation/devicetree/bindings/net/wireless/qcom,ath10k.txt
> > qcom,ath10k-calibration-data
> > 
> > Documentation/devicetree/bindings/gpio/gpio-pcf857x.txt
> > lines-initial-states
> 
> It'd rather be better to fix the drivers and remove the properties
> from these found device tree binding descriptions.

no sure if it is possible. WiFi calibration data is kind of initval too.

> > 
> > Please fixme if I miss something.
> 
> Why is GPIO hogging mechanism not good enough for your purpose?

Becouse it should not permanently hog a gpio. The "Hogging" should be
released as soon as some driver will request it.

Right now, if I define gpio-hog, boot loader will configure it and start
linux. But linux will never let it free.

If you have other suggestions which fit to this use case, please tell
me. I assume, right now I'm just blind.

Other way, I can imagine is to create real device nodes which use this
gpios. Compatible for this devices will be like this:
some_gpio_holder: gpio@0 {
	compatible = "gpio-for-userspace";
	gpio = <&gpio1 5 GPIO_ACTIVE_HIGH>;
};

Boot loader will configure it as needed, an linux will do nothing with
it so it can be used over /dev/gpio interface.

> --
> With best wishes,
> Vladimir

-- 
Pengutronix e.K.                           |                             |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |
Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0    |
Amtsgericht Hildesheim, HRA 2686           | Fax:   +49-5121-206917-5555 |

Re: [PATCH v1 1/1] gpio: of: provide option generic property for initial line states

[Vladimir Zapolskiy]

Hi Oleksij,

On 06/15/2017 08:56 AM, Oleksij Rempel wrote:
> Hi Vladimir,
> 
> On Sun, Jun 11, 2017 at 10:57:18PM +0300, Vladimir Zapolskiy wrote:
>> Hi Oleksij,
>>
>> On 06/11/2017 09:19 AM, Oleksij Rempel wrote:
>>> Hi Rob,
>>>
>>> On Fri, Jun 09, 2017 at 10:41:30AM -0500, Rob Herring wrote:
>>>> On Fri, Jun 9, 2017 at 9:16 AM, Oleksij Rempel <o.rempel@pengutronix.de> wrote:
>>>>> This property is needed for barebox or may be other bootloaders
>>>>> to set proper gpio configuration as early as possible.
>>>>>
>>>>> This example is mainly based on "lines-initial-states" property
>>>>> from this binding documentation:
>>>>> Documentation/devicetree/bindings/gpio/gpio-pcf857x.txt
>>>>
>>>> Don't we have a binding for this already based on gpio-hogs.
>>>
>>> Markus Pargmann was working on this topic before and suddenly was not
>>> able to finish it.
>>
>> that's fine, but the proposed extension is supposedly not wanted.
> 
> :(

No worries, we're in the discussion and 'supposedly' was a meaningful
word :)

>>> I found only some not finished discussions and no code or documentation
>>> in linux kernel upstream.
>>>
>>> So far, I was able to find fallowing patches and discussions:
>>> patch 23.08.2015, last comment 11.05.2017:
>>> https://patchwork.kernel.org/patch/7096721/
>>>
>>> patch 23.02.2016, last comment 09.03.2016:
>>> https://patchwork.ozlabs.org/patch/586743/
>>>
>>> Since there was objections about node-like design for gpio-initval, I
>>> provided an array property, which is similar to initval properties already used
>>> for different other device nodes. For example:
>>>
>>> Documentation/devicetree/bindings/net/wireless/qcom,ath10k.txt
>>> qcom,ath10k-calibration-data
>>>
>>> Documentation/devicetree/bindings/gpio/gpio-pcf857x.txt
>>> lines-initial-states
>>
>> It'd rather be better to fix the drivers and remove the properties
>> from these found device tree binding descriptions.
> 
> no sure if it is possible. WiFi calibration data is kind of initval too.

Sorry, I have no idea about the ath10k calibration data and its
connection to the GPIO framework.

>>>
>>> Please fixme if I miss something.
>>
>> Why is GPIO hogging mechanism not good enough for your purpose?
> 
> Becouse it should not permanently hog a gpio. The "Hogging" should be
> released as soon as some driver will request it.
> 
> Right now, if I define gpio-hog, boot loader will configure it and start
> linux. But linux will never let it free.
> 
> If you have other suggestions which fit to this use case, please tell
> me. I assume, right now I'm just blind.

Ok, I'll meditate on it.

> Other way, I can imagine is to create real device nodes which use this
> gpios. Compatible for this devices will be like this:
> some_gpio_holder: gpio@0 {
> 	compatible = "gpio-for-userspace";
> 	gpio = <&gpio1 5 GPIO_ACTIVE_HIGH>;
> };

Generally it might be a good option, because if GPIOs are essentially
needed to be preset, I can conclude there are some ICs to which these
GPIOs are connected, thus drivers of these ICs can become GPIO consumers
and get a proper description in a board DTB.

> 
> Boot loader will configure it as needed, an linux will do nothing with
> it so it can be used over /dev/gpio interface.

As I read it from Documentation/gpio/sysfs.txt generic interface(s)
to control GPIOs is a last resort, it is not clear if you want a new
feature for all possible consumers or just userspace consumers.

--
With best wishes,
Vladimir