Subject: [linux-sunxi] Re: [PATCH 5/5] ARM: dts: sun5i: Add backlight node to sun5i-q8-common.dtsi

From: [email-masked] (Hans de Goede)
Date: Sun, 20 Sep 2015 11:21:54 -0400

Hi,

On 09/20/2015 11:14 AM, Hans de Goede wrote:
> Hi,
>
> On 09/20/2015 10:46 AM, Chen-Yu Tsai wrote:
>> On Sun, Sep 20, 2015 at 8:30 PM, Hans de Goede <[email-masked]> wrote:
>>> All A13 based q8 formfactor tablets use the same backlight setup, add
>>> a backlight devicetree node for controlling the backlight on these devices.
>>>
>>> Signed-off-by: Hans de Goede <[email-masked]>
>>> ---
>>>   arch/arm/boot/dts/sun5i-q8-common.dtsi | 11 +++++++++++
>>>   1 file changed, 11 insertions(+)
>>>
>>> diff --git a/arch/arm/boot/dts/sun5i-q8-common.dtsi b/arch/arm/boot/dts/sun5i-q8-common.dtsi
>>> index 0641d68..76a5204 100644
>>> --- a/arch/arm/boot/dts/sun5i-q8-common.dtsi
>>> +++ b/arch/arm/boot/dts/sun5i-q8-common.dtsi
>>> @@ -41,11 +41,22 @@
>>>    */
>>>   #include "sunxi-q8-common.dtsi"
>>>
>>> +#include <dt-bindings/pwm/pwm.h>
>>> +
>>>   / {
>>>          aliases {
>>>                  serial0 = &uart1;
>>>          };
>>>
>>> +       backlight: backlight {
>>> +               compatible = "pwm-backlight";
>>> +               pwms = <&pwm 0 50000 PWM_POLARITY_INVERTED>;
>>> +               brightness-levels = <0 10 20 30 40 50 60 70 80 90 100>;
>>> +               default-brightness-level = <8>;
>>> +               /* TODO: backlight uses axp gpio1 as enable pin */
>>> +               /* TODO: backlight is powered by AXP209 DCDC1SW */
>>
>> There's no DCDC1SW on AXP209. The reference design shows the backlight
>> regulator is powered directly from IPSOUT,
>
> Ah, right, I'll do a v2 dropping this comment line.
>
>  > but the PWM pullup is powered
>> by LCD-VCC,  which itself is enabled by AXP209 GPIO0.
>>
>> Would that be the case, or maybe closer, given we don't have schematics?
>
> gpio0 needs to be driven high to get the backlight to lite up, that
> is pretty much all I know.

Correction, gpio1. I guess that pullup is only there to keep the backlight
off while the pwm pin is still muxed as input, rather then pwm-output.

Regards,

Hans