pwm based backlight driver support for the lcd panel

[ask]

Hi all,

I am using imx287 processor based board for one of my Infotainment project. In this product lcd panel backlight is controlling by PWM4.  I tried to enable the CONFIG_BACKLIGHT_PWM and HAVE_PWM  options, but those are not available in my ltib setup.  I tried to build these options by modifying the corresponding make files (drivers/video/backlight/Makefile  and arch/arm/plat-mxc) and ended up with build erros. Please let me know whether I am following wrong approach?

[igorpadykov]

Hi ashok

please refer to attached Linux Manual

Chapter 28 LED Pulse Width Modulator (PWM) Driver

Examples for two control the brightness of the LEDs on the MX28 EVK:

# ./devices/platform/mxs-leds.0/leds/led-pwm0

# ./devices/platform/mxs-leds.0/leds/led-pwm1

Usable settings are 0 to 127

echo 127 > /sys/devices/platform/mxs-leds.0/leds/led-pwm0/brightness        //Led0 On

echo 0 > /sys/devices/platform/mxs-leds.0/leds/led-pwm0/brightness          //Led0 Off

echo 127 > /sys/devices/platform/mxs-leds.0/leds/led-pwm1/brightness      //Led1 On

echo 0 > /sys/devices/platform/mxs-leds.0/leds/led-pwm1/brightness        //Led1 Off

Best regards

igor

[ask]

!Hi igorpadykov,

Thanks for your reply

I could able to controld the lcd panel brightness using led-mxs-pwm functionality.

[igorpadykov]

Hi ashok

Please look below links for pwm

https://github.com/boundarydevices/linux-imx6/commit/63b106e30a42e5ee89c4c7d

0644e853f013276db

https://community.freescale.com/message/433746#433746

Best regards

igor

[fabio_estevam]

In a 3.17 kernel you can see arch/arm/boot/dts/imx28-evk.dts and search for the 'backlight' node.

It is controlled by PWM2 and you can easily change it to PWM4 as per your needs.

[ask]

Hi  Fabio,

Please can you share me the link for 3.17 kernel.

Linux kernel I am using 2.6.35.3. I am following chapters 9,10, and 11 of the  MX28_EVK_Linux_Reference_Manual.pdf and also refering drivers/video/mxs/lcd_43wvf1g.c file. It was configured to pwm2 and changed it to pwm4 as per my needs. I also got sysfs entries as follows.

/sys/devices/platform/mxs-bl.0/backlight/mxs-bl$ ls

actual_brightness  brightness         max_brightness     subsystem

bl_power           device             power              uevent

Default values are as follows:

/sys/devices/platform/mxs-bl.0/backlight/mxs-bl$ cat brightness

50

/sys/devices/platform/mxs-bl.0/backlight/mxs-bl$ cat bl_power

1

I changed bl_power to 0 brightness to 100, there is no effect on the display. I am not seeing backlight.

Please let me know do we have to configure any other settings.

If we change it gpio it is working fine. I am able to see the backlight.

Thanks and Regards

Ashok .K

[fabio_estevam]

You can get it from here:

https://www.kernel.org/