[PATCH V3] ARM: dts: da850-evm: Enable LCD and Backlight

[nsekhar@ti.com (Sekhar Nori)]

On Monday 14 May 2018 11:34 PM, Adam Ford wrote:
> On Mon, May 14, 2018 at 7:35 AM, Sekhar Nori <nsekhar@ti.com> wrote:
>> On Monday 14 May 2018 04:22 PM, Adam Ford wrote:
>>> On Mon, May 14, 2018 at 12:29 AM, Sekhar Nori <nsekhar@ti.com> wrote:
>>>> Hi Adam,
> 
> Added Tomi, Laurent, and Jyri for feedback.
> 
>>>>
>>>> On Monday 14 May 2018 04:50 AM, Adam Ford wrote:
>>>>> When using the board files the LCD works, but not with the DT.
>>>>> This adds enables the original da850-evm to work with the same
>>>>> LCD in device tree mode.
>>>>>
>>>>> The EVM has a gpio for the regulator and a gpio enable.  The LCD and
>>>>> the vpif display pins are mutually exclusive, so if using the LCD,
>>>>> do not load the vpif driver.
>>>>
>>>> Its not sufficient just note this in patch description.
>>>>
>>>> a) Disable (status = "disabled") the VPIF node which clashes for pins
>>>> with LCD.
>>>> b) Add a comment on top of the status = "disabled" giving information on
>>>> how user can enable it (disable lcdc node and then change to status =
>>>> "okay").
>>>>
>>>>>
>>>>> Signed-off-by: Adam Ford <aford173@gmail.com>
>>>>> ---
>>>>> V3:  Fix errant GPIO, label GPIO pins, and rename the regulator to be more explict to
>>>>>      backlight which better matches the schematic.  Updated the description to explain
>>>>>      that it cannot be used at the same time as the vpif driver.
>>>>>
>>>>> V2:  Add regulator and GPIO enable pins. Remove PWM backlight and replace with GPIO
>>>>>
>>>>> diff --git a/arch/arm/boot/dts/da850-evm.dts b/arch/arm/boot/dts/da850-evm.dts
>>>>> index 2e817da37fdb..3f1c8be07efe 100644
>>>>> --- a/arch/arm/boot/dts/da850-evm.dts
>>>>> +++ b/arch/arm/boot/dts/da850-evm.dts
>>>>> @@ -27,6 +27,50 @@
>>>>>               spi0 = &spi1;
>>>>>       };
>>>>>
>>>>> +     backlight {
>>>>> +             compatible = "gpio-backlight";
>>>>> +             enable-gpios = <&gpio 7 GPIO_ACTIVE_HIGH>; /* GP0[7] */
>>>>
>>>> The gpio-backlight binding does not describe a property called
>>>> enable-gpios. It should just be gpios.
>>>
>>> I will fix that.
>>>
>>>>
>>>> a) Are you using gpio-backlight because you are not able to get the PWM
>>>> to work?
>>>>
>>> Yes,  You told me not to worry about doing a PWM backlight because the
>>> legacy board does not PWM either.
>>
>> Yeah, I meant not to add backlight control till the time we are able to
>> get it working using PWM. Is this needed for the basic LCD functionality
>> to work? I would like to avoid the churn of adding it using GPIO now and
>> changing to PWM later, if possible.
>>
>>>
>>>> b) What is GP0[7] connected to in the schematic you have? In the
>>>> schematic I have I see LCD_PWM0 is connected to
>>>> SPI1_SCS[0]/EPWM1B/GP2[14]/TM64P3_IN12.
>>>
>>> I have schematic 1016572 dated Wednesday, August 18, 2010.  According
>>> to it, AXR15 / EPWMN0_TZ[0] / ECAP2_APWM2 / GPIO0[7] connects to U25,
>>> Pin 46 to generate M_LCD_PWM0.  You might have one of the early,
>>> pre-release versions.
>>
>> Ah, okay. In your schematic, is GP2[14] connected to anything?
>>
>>>
>>>>
>>>> c) The /* GP0[7] */ comment is not really useful on its own as it can be
>>>> computed. What I wanted to see is the schematic symbol like "LCD_PWM0".
>>>> Same for other places like this below.
>>>
>>> I can do that.
>>>>
>>>>> @@ -35,6 +79,16 @@
>>>>>               regulator-boot-on;
>>>>>       };
>>>>>
>>>>> +     backlight_reg: backlight-regulator {
>>>>> +             compatible = "regulator-fixed";
>>>>> +             regulator-name = "lcd_backlight_pwr";
>>>>> +             regulator-min-microvolt = <3300000>;
>>>>> +             regulator-max-microvolt = <3300000>;
>>>>> +             gpio = <&gpio 47 GPIO_ACTIVE_HIGH>; /* GP2[15] */
>>>>> +             regulator-always-on;
>>>>
>>>> Why should this regulator never be disabled?
>>>
>>> The gpio-backlight does not have a way that I can see to associate the
>>> regulator to it.  I read through the bindings, but I didn't see an
>>> option to associate a regulator it.  I use this regulator to drive
>>> lcd_backlight_pwr and the backlight driver to write lcd_pwm0.  Without
>>> this option, the system disables lcd_backlight_pwr and the screen is
>>> blank
>>
>> It sounds like this is a hack to enable backlight on this board. I think
>> either the backlight driver needs to gain functionality to enable the
>> GPIO. Or backlight could be treated as part of the panel and enabled
>> using enable-gpios property in the panel. TBH, I will be okay either
>> way. Can you check with Jyri, Tomi and rest of the DRM folks on what
>> should be right way of dealing with this?
> 
> Per your request I added them into this thread.  I added Tomi, Jyri,
> and Laurent to this as Laurent's name is associated with the gpio
> backlight driver.

Okay. The reason I did not loop them in myself is because I thought a
fresh thread with background will be better. But okay.

> I am not sure why you think it's a hack.  I pulled up the schematic
> for the LCD to see what it's doing, and the  lcd_backlight_pwr pin
> controls the power-on sequence of the back-light controller.  Without
> this, there is no power, so it seems to me that the 'regulator-fixed'
> device is the correct way to do it.

Not questioning modeling the GPIO as a regulator.

> 
> The separate pin associated to the gpio is used to tell the backlight
> IC to actually turn on/off the back-light.  Ideally it seems like it
> would nice to have the gpio-backlight driver be able to specify the
> regulator, so when the backlight is in use, it would power the
> regulator, but until that's available, the it seems like
> 'regulator-always-on' is the way to make it stay on.

We need to add support for this in backlight driver. Using
regulator-always-on to paper over this lack of support in backlight
driver is what I am calling a hack. 'regulator-always-on' means the
regulator cannot be turned off. Thats certainly not the case as you have
pointed out.

Thanks,
Sekhar