Re: LCD with PWM backlight doesn't seem to work with atmel-hlcdc driver

[Pedro Aguilar <p.aguilar@nethix.com>]

Hi,

Just to clarify that we solved this issue a couple of days after the 
original email.

The problem was that we wanted to use for the LCD PWM (backlight) a 
DIV_1 that the driver does not allow because of an issue with the Atmel 
SAMA5D34 (the atmel-hlcdc driver handles it correctly, see section 
60.4.1 in the datasheet).

With the other DIV_2-64 everything is working fine.

Regards.
--
Pedro Aguilar

Nethix s.r.l
Via dei Pini, 21
31033 Castelfranco Veneto (TV)
T. +39 0423 770750 - F. +39 0423 770749
www.nethix.com

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On 01/11/2016 07:38 PM, Pedro Aguilar wrote:
> Hi,
>
> I'm working on a custom board based on the Atmel sama5d3_ek. I have an
> LCD (T430T01W01A from Cristal Clear Technology) that has a PWM backlight
> and it should be supported in the device tree files (sama5d34ek_pda4)
> and the panel_simple driver since it's compatible with the already
> supported Innolux at043tn24.
>
> When booting I see in the LCD the Atmel logo with some info, this means
> that electrically the board and the LCD work fine.
>
> I built the LCD modules (pwm_atmel_hlcdc, backlight, pwm_bl,
> panel_simple and atmel_hlcdc_dc) out of the kernel and modprobe'd them
> manually after booting:
>
> # modprobe pwm_atmel_hlcdc
> # modprobe backlight
> # modprobe pwm_bl
> backlight_device_register: name=backlight
> # modprobe panel_simple
> # modprobe atmel_hlcdc_dc
> [drm] Supports vblank timestamp caching Rev 2 (21.10.2013).
> [drm] No driver support for vblank timestamp query.
> atmel-hlcdc-display-controller atmel-hlcdc-dc: DRM device successfully
> registered
> atmel-hlcdc-display-controller atmel-hlcdc-dc: fb0: frame buffer device
> atmel-hlcdc-display-controller atmel-hlcdc-dc: registered panic notifier
> #
>
> When modprobing pwm_bl the LCD seemed to be turned-off (the logo from
> uboot goes away) and the the PWM backlight is off.
>
> I tried several user space programs (fb-set-rect and Qt5 examples built
> with buildroot) but the LCD seemed dead. All the entries in sysfs, such
> as /sys/class/backlight were present, but didn't work. For example, I
> tried to power on/off the backlight
>
> echo 1 > /sys/class/backlight/backlight/bl_power
> echo 0 > /sys/class/backlight/backlight/bl_power
>
> but it didn't work. The same with the brightness.
>
> The datasheet of this LCD and the Innolux LCD are equivalent.
>
> It seems that there is something related to the voltage in the PWM
> backlight or panel regulators?
>
> Do you have any idea/hint of what could cause this issue?
>
> Thanks!
>
> --
> Pedro Aguilar
> --
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