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LVDS and HDMI in iMX6 DualLite

Question asked by Julio Cruz on Oct 31, 2018
Latest reply on Nov 4, 2018 by Julio Cruz

Hello,

A custom board included an iMX6 DualLite with a LVDS and HDMI display split as below:

  • LVDS: IPU1, display 0
  • HDMI (optional): IPU1, display 1

The LVDS is working properly while the HDMI display is not working. The test criteria is based on the imx-test autorun-fb0.sh

I has been reviewing the different variables, as the HDMI display properties, hardware schematic and layout, u-boot, kernel drivers and discussions (here and there) regarding HDMI and dual display using the iMX6 series.

 

Due to the big quantity of variables that could be involved, I will share many of those through pastebin.com trying to keep the post short.

Configuration:

Booting (log):

After boot (setup):

Testing:

Display:

 

Comments:

  1. The EDID data seem OK and match with the info when the display is connected to a PC with Windows 10, as well an online EDID reader
  2. The frame buffer devices are as expected, two [main and overlay] for the first device (LDVS) and one for the HDMI. Any difference (function or performance) if the HDMI is first with fb0 and fb1 and LVDS second with fb2?
  3. The kernel detect when the HDMI cable is connected and disconnected (see similar log in HDMI test result log during the imx-tests, where the fb2 is blank)
  4. The frame buffer setup (based on fbset) is as expected and similar to the PC in WIndows 10
  5. During the testing with the HDMI display, the log show an error (multiple times) in the line #71 [echo 0,$i > /sys/class/graphics/$1/pan]: echo: write error: Invalid argumentAlthough the screen does not show anything, will it be worth checking this error?
  6. During booting there is not sound card for HDMI registered. aplay -l command show only the sgtl5000 codec card and the log show mxc_hdmi 20e0000.hdmi_video: hdmi_enable_audio_clk related with audio & HDMI. Any thoughts regarding HDMI audio?
  7. Once the test is performed in fb2, the test in fb0 not update the display anymore. After reboot, the fb0 is OK and the test result is as expected.
  8. The clock frequency show in the system log [mxc_hdmi 20e0000.hdmi_video: final pixclk = 74250000] match the value obtained with a scope in the connector pin.

I appreciated any suggestion regarding this situation. I've run out of options or variables to look at.

Thanks

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