HDMI issue in i.MX6Q board

[pratik_manvar]

Hi NXP-Team,

We are using i.MX6Q based custom board.
We have a MIPI LCD which is connected with processor through HDMI and using HDMI to MIPI bridge Lontium IC in between.

We are facing strange issue. During boot up, u-boot logo is displayed every time. But, in some of the LCDs, there is no display on LCD (LCD is blank) after kernel starts.
But some LCDs are working fine and got display every-time. LCDs are operating on 71Mhz pixel clock.

We don't understand why there is display every-time in u-boot and no display after kenrel starts for some LCDs.

Also, one more observation is that, not working LCDs are working fine on 27Mhz pixel clock (of course there is a flicker).

Please help us out, what could be the issue and what is the difference in HDMI initialisation between U-boot and kernel?

Thanks,
Pratik Manvar

[pratik_manvar]

Hi Igor,

Thanks for the support.

We are still debugging and need you help for below points.

1. The LCD power-up/init sequence seems OK (even for the LCDs which remain blank after kernel starts).
We have debug this by enabling the white screen after LCD init sequence is done.
The white screen is observed on all the LCDs during boot-up.
But, QT application is not displayed in some of the LCDs after boot-up.

2. We can see u-boot logo in all the LCDs everytime.
After kernel starts some LCDs remain black (no display of QT application).
But, other LCDs are working fine and display QT application after boot-up.

3. In LCDs which remain black after boot-up (no display of QT application),
when we touch on screen, it generates application events (e.g., button press event) as per QT GUI.
What could be the reason? Is that mean, framebuffer is having the contents of QT app,
but it is not able to display for some reason?

4. We have gone through the discussion uboot logo color is not normal  as you suggested,
but still we are not clear about the difference in HDMI initialisation between U-boot and kernel.

Can you please help us to understand the difference in HDMI initialisation in kernel which could lead to above behaviour?

Thank You.

Regards,
Pratik Manvar

[igorpadykov]

Hi Pratik

issue may be related to LCD power-up sequence, some panels

require specific timings so one can recheck it with oscilloscope.

Regarding "difference in HDMI initialisation between U-boot and kernel?" -

one can look at discussion on https://community.nxp.com/thread/392013 

Best regards
igor
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