iMX6q Sabre Auto - GPIO Pin number for LVDS backlight enable

[akhilgopi]

Hello,

Backlight of LVDS display connected to iMX6 is going off(issue) during android kernel bootup. On uboot LVDS backlight is available(no issue). 

On backlight driver "drivers/video/backlight/pwm_bl.c" inside "pwm_backlight_probe()" function "gpio_is_valid(data->enable_gpio)" returns error. So "pb->enable_gpio" descriptor is unavailable and "gpiod_direction_output(pb->enable_gpio, 1);"  could not set. 

I think if we specify the GPIO pin number of backlight enable pin, then we can set its direction and make it high for back light. Please comment on this and let me know the GPIO Number for LVDS backlight enable.

[akhilgopi]

Thank you again Igor.

We tried with "IMX6_M6.0.1_2.1.0_ANDROID_DEMO_AI_BSP" demo image using "Android_Quick_Start_Guide.pdf" document Number: AQSUG, Rev. M6.0.1_2.1.0_1, 02/2017".

We found this backlight issue on demo image itself. The uBoot splash screen is OK with backlight, But while booting the android screens are also available but NO backlight.

The BACKLITE_ON pin on J3 connector going logic low on android kernel bootup.

We use a custom LVDS display on which we need BACKLITE_ON pin on J3 connector to be high to enable back light.

It would be really helpful if you can suggest how to turn on  BACKLITE_ON pin.

[igorpadykov]

Hi Akhil

for gpio numbering one can look for example at

Definitive GPIO guide - Studio Kousagi Wiki 

however this depends on schematic, for sabre ai board one can look at its schematic on

Schematics (5)
Design files for i.MX 6Quad and i.MX 6DualLite CPU1 Cards
Design files for Base Board (REV E)

http://www.nxp.com/products/software-and-tools/hardware-development-tools/sabre-development-system/s...

Best regards
igor
-----------------------------------------------------------------------------------------------------------------------
Note: If this post answers your question, please click the Correct Answer button. Thank you!
-----------------------------------------------------------------------------------------------------------------------

[akhilgopi]

Thank you very much igor.

As per the guidance, we checked the schematic of  "LVDS Display" (Page No.16) on "SPF-27925_F2.pdf"  document from design files of iMX6q Sabre AI. From that diagram we could see the LVDS0 connector (J13) on which pin number 1 (BACKLITE_ON(PORT_EXP_A0)) is our consideration. 

As the part of analysis on backlight turnoff issue, we checked the pin 1(BACKLITE_ON) of J13  connector  using multimeter. The multimeter shows 3.3V in uboot stage and going to 0V while starting (android M6)kernel boot. 

That is, after (android M6) kernel booting up the BACKLITE_ON pin going to low, which we suspect as backlight turn off issue. 

Our assumption is, to enable backlight,  pin 1(BACKLITE_ON) should be high. But BACKLITE_ON is controlled by iMX6 via "Port Expander A" by I2C.  

Could you please suggest how to make pin 1(BACKLITE_ON) to high from kernel.

[igorpadykov]

Hi Akhil

could you try with Demo Image

http://www.nxp.com/webapp/Download?colCode=IMX6_M6.0.1_2.1.0_AN_DEMO_AI_BSP&appType=license&location... 

Best regards
igor