devicetree bindings for a generic led-based backlight driver

devicetree bindings for a generic led-based backlight driver

[Jean-Jacques Hiblot]

Hi,

A few years ago (2015), Tomi Valkeinen posted a series implementing a 
backlight driver on top of a LED device.

https://patchwork.kernel.org/patch/7293991/
https://patchwork.kernel.org/patch/7294001/
https://patchwork.kernel.org/patch/7293981/

The discussion stopped  because he lacked the time to work on it.

I will be taking over the task and, before heading in the wrong 
direction, wanted a confirmation that the binding Tomi last proposed in 
hist last email was indeed the preferred option.

It will probably require some modifications in the LED core to create 
the right kind of led-device (normal, flash or backlight) based on the 
compatible option.

Thanks for your feedback

JJ

Re: devicetree bindings for a generic led-based backlight driver

[Jacek Anaszewski]

Hi Jean,

On 6/26/19 5:34 PM, Jean-Jacques Hiblot wrote:
> Hi,
> 
> A few years ago (2015), Tomi Valkeinen posted a series implementing a
> backlight driver on top of a LED device.
> 
> https://patchwork.kernel.org/patch/7293991/
> https://patchwork.kernel.org/patch/7294001/
> https://patchwork.kernel.org/patch/7293981/
> 
> The discussion stopped  because he lacked the time to work on it.
> 
> I will be taking over the task and, before heading in the wrong
> direction, wanted a confirmation that the binding Tomi last proposed in
> hist last email was indeed the preferred option.
> 
> It will probably require some modifications in the LED core to create
> the right kind of led-device (normal, flash or backlight) based on the
> compatible option.

I recall that discussion. I gave my ack for the LED changes but
now we have more LED people that might want to look into that.

Regarding the bindings we have pending LED naming patch set,
that deprecates DT label property [0] and introduces standardized
LED functions.

[0] https://lkml.org/lkml/2019/6/9/728

-- 
Best regards,
Jacek Anaszewski

Re: devicetree bindings for a generic led-based backlight driver

[Jean-Jacques Hiblot]

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Hi Jacek,

On 26/06/2019 20:55, Jacek Anaszewski wrote:
> Hi Jean,
>
> On 6/26/19 5:34 PM, Jean-Jacques Hiblot wrote:
>> Hi,
>>
>> A few years ago (2015), Tomi Valkeinen posted a series implementing a
>> backlight driver on top of a LED device.
>>
>> https://patchwork.kernel.org/patch/7293991/
>> https://patchwork.kernel.org/patch/7294001/
>> https://patchwork.kernel.org/patch/7293981/
>>
>> The discussion stopped  because he lacked the time to work on it.
>>
>> I will be taking over the task and, before heading in the wrong
>> direction, wanted a confirmation that the binding Tomi last proposed in
>> hist last email was indeed the preferred option.
>>
>> It will probably require some modifications in the LED core to create
>> the right kind of led-device (normal, flash or backlight) based on the
>> compatible option.
> I recall that discussion. I gave my ack for the LED changes but
> now we have more LED people that might want to look into that.

Regarding the LED bindings as discussed by Tom and Rob in 
https://patchwork.kernel.org/patch/7293991/, what do you think of using 
a 'compatible' string to make a LED device also a backlight or a flash LED ?

Here is the example from Tomi at the end of the discussion:

/* tlc59108 is an i2c device */
tlc59116@40 {
	#address-cells = <1>;
	#size-cells = <0>;
	compatible = "ti,tlc59108";
	reg = <0x40>;

	wan@0 {
		label = "wrt1900ac:amber:wan";
		reg = <0x0>;
	};

	bl@2 {
		label = "backlight";
		reg = <0x2>;

		compatible = "led-backlight";
		brightness-levels = <0 243 245 247 248 249 251 252 255>;
		default-brightness-level = <8>;

		enable-gpios = <&pcf_lcd 13 GPIO_ACTIVE_LOW>;
	};
};

>
> Regarding the bindings we have pending LED naming patch set,
> that deprecates DT label property [0] and introduces standardized
> LED functions.
>
> [0] https://lkml.org/lkml/2019/6/9/728

Thanks for the info.



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Re: devicetree bindings for a generic led-based backlight driver

[Jacek Anaszewski]

Hi Jean,

Side note: please use plain text in your messages.

On 6/27/19 3:14 PM, Jean-Jacques Hiblot wrote:
> Hi Jacek,
> 
> On 26/06/2019 20:55, Jacek Anaszewski wrote:
>> Hi Jean,
>>
>> On 6/26/19 5:34 PM, Jean-Jacques Hiblot wrote:
>>> Hi,
>>>
>>> A few years ago (2015), Tomi Valkeinen posted a series implementing a
>>> backlight driver on top of a LED device.
>>>
>>> https://patchwork.kernel.org/patch/7293991/
>>> https://patchwork.kernel.org/patch/7294001/
>>> https://patchwork.kernel.org/patch/7293981/
>>>
>>> The discussion stopped  because he lacked the time to work on it.
>>>
>>> I will be taking over the task and, before heading in the wrong
>>> direction, wanted a confirmation that the binding Tomi last proposed in
>>> hist last email was indeed the preferred option.
>>>
>>> It will probably require some modifications in the LED core to create
>>> the right kind of led-device (normal, flash or backlight) based on the
>>> compatible option.
>> I recall that discussion. I gave my ack for the LED changes but
>> now we have more LED people that might want to look into that.
> 
> Regarding the LED bindings as discussed by Tom and Rob in
> https://patchwork.kernel.org/patch/7293991/, what do you think of using
> a 'compatible' string to make a LED device also a backlight or a flash LED ?

After going through the referenced discussion and refreshing my memory
it looks to me the most reasonable way to go for backlight case.

Nevertheless I'd not tamper at LED flash support - if it's not broken,
don't fix it.

Best regards,
Jacek Anaszewski

> Here is the example from Tomi at the end of the discussion:
> 
> /* tlc59108 is an i2c device */
> tlc59116@40 {
> 	#address-cells = <1>;
> 	#size-cells = <0>;
> 	compatible = "ti,tlc59108";
> 	reg = <0x40>;
> 
> 	wan@0 {
> 		label = "wrt1900ac:amber:wan";
> 		reg = <0x0>;
> 	};
> 
> 	bl@2 {
> 		label = "backlight";
> 		reg = <0x2>;
> 
> 		compatible = "led-backlight";
> 		brightness-levels = <0 243 245 247 248 249 251 252 255>;
> 		default-brightness-level = <8>;
> 
> 		enable-gpios = <&pcf_lcd 13 GPIO_ACTIVE_LOW>;
> 	};
> };
> 
>> Regarding the bindings we have pending LED naming patch set,
>> that deprecates DT label property [0] and introduces standardized
>> LED functions.
>>
>> [0] https://lkml.org/lkml/2019/6/9/728
> 
> Thanks for the info.
> 
> 

Re: devicetree bindings for a generic led-based backlight driver

[Pavel Machek]

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Hi!

> >>> A few years ago (2015), Tomi Valkeinen posted a series implementing a
> >>> backlight driver on top of a LED device.
> >>>
> >>> https://patchwork.kernel.org/patch/7293991/
> >>> https://patchwork.kernel.org/patch/7294001/
> >>> https://patchwork.kernel.org/patch/7293981/
> >>>
> >>> The discussion stopped  because he lacked the time to work on it.
> >>>
> >>> I will be taking over the task and, before heading in the wrong
> >>> direction, wanted a confirmation that the binding Tomi last proposed in
> >>> hist last email was indeed the preferred option.
> >>>
> >>> It will probably require some modifications in the LED core to create
> >>> the right kind of led-device (normal, flash or backlight) based on the
> >>> compatible option.
> >> I recall that discussion. I gave my ack for the LED changes but
> >> now we have more LED people that might want to look into that.
> > 
> > Regarding the LED bindings as discussed by Tom and Rob in
> > https://patchwork.kernel.org/patch/7293991/, what do you think of using
> > a 'compatible' string to make a LED device also a backlight or a flash LED ?
> 
> After going through the referenced discussion and refreshing my memory
> it looks to me the most reasonable way to go for backlight case.
> 
> Nevertheless I'd not tamper at LED flash support - if it's not broken,
> don't fix it.
> 
> Best regards,
> Jacek Anaszewski
> 
> > Here is the example from Tomi at the end of the discussion:
> > 
> > /* tlc59108 is an i2c device */
> > tlc59116@40 {
> > 	#address-cells = <1>;
> > 	#size-cells = <0>;
> > 	compatible = "ti,tlc59108";
> > 	reg = <0x40>;
> > 
> > 	wan@0 {
> > 		label = "wrt1900ac:amber:wan";
> > 		reg = <0x0>;
> > 	};
> > 
> > 	bl@2 {
> > 		label = "backlight";
> > 		reg = <0x2>;
> > 
> > 		compatible = "led-backlight";
> > 		brightness-levels = <0 243 245 247 248 249 251 252 255>;
> > 		default-brightness-level = <8>;
> > 
> > 		enable-gpios = <&pcf_lcd 13 GPIO_ACTIVE_LOW>;

So... this needs some kind of reference to display it belongs to,
right?

									Pavel

-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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Re: devicetree bindings for a generic led-based backlight driver

[Jean-Jacques Hiblot]

Hi Pavel

On 06/07/2019 17:19, Pavel Machek wrote:
> Hi!
>
>>>>> A few years ago (2015), Tomi Valkeinen posted a series implementing a
>>>>> backlight driver on top of a LED device.
>>>>>
>>>>> https://patchwork.kernel.org/patch/7293991/
>>>>> https://patchwork.kernel.org/patch/7294001/
>>>>> https://patchwork.kernel.org/patch/7293981/
>>>>>
>>>>> The discussion stopped� because he lacked the time to work on it.
>>>>>
>>>>> I will be taking over the task and, before heading in the wrong
>>>>> direction, wanted a confirmation that the binding Tomi last proposed in
>>>>> hist last email was indeed the preferred option.
>>>>>
>>>>> It will probably require some modifications in the LED core to create
>>>>> the right kind of led-device (normal, flash or backlight) based on the
>>>>> compatible option.
>>>> I recall that discussion. I gave my ack for the LED changes but
>>>> now we have more LED people that might want to look into that.
>>> Regarding the LED bindings as discussed by Tom and Rob in
>>> https://patchwork.kernel.org/patch/7293991/, what do you think of using
>>> a 'compatible' string to make a LED device also a backlight or a flash LED ?
>> After going through the referenced discussion and refreshing my memory
>> it looks to me the most reasonable way to go for backlight case.
>>
>> Nevertheless I'd not tamper at LED flash support - if it's not broken,
>> don't fix it.
>>
>> Best regards,
>> Jacek Anaszewski
>>
>>> Here is the example from Tomi at the end of the discussion:
>>>
>>> /* tlc59108 is an i2c device */
>>> tlc59116@40 {
>>> 	#address-cells = <1>;
>>> 	#size-cells = <0>;
>>> 	compatible = "ti,tlc59108";
>>> 	reg = <0x40>;
>>>
>>> 	wan@0 {
>>> 		label = "wrt1900ac:amber:wan";
>>> 		reg = <0x0>;
>>> 	};
>>>
>>> 	bl@2 {
>>> 		label = "backlight";
>>> 		reg = <0x2>;
>>>
>>> 		compatible = "led-backlight";
>>> 		brightness-levels = <0 243 245 247 248 249 251 252 255>;
>>> 		default-brightness-level = <8>;
>>>
>>> 		enable-gpios = <&pcf_lcd 13 GPIO_ACTIVE_LOW>;
> So... this needs some kind of reference to display it belongs to,
> right?

This is the reverse. The display uses a reference the backlight.

JJ

>
> 									Pavel
>