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

[Adam Ford]

On Mon, May 14, 2018 at 7:35 AM, Sekhar Nori <nsekhar at 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 at 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 at 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.

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.

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.

Laurent, Jyri, Tomi, do you have any thoughts on this matter?

Thanks,

adam
>
> Thanks,
> Sekhar