7" 800x400 HDMI Backpack with touch no video good LED

EL Wire/Tape/Panels, LEDs, pixels and strips, LCDs and TFTs, etc products from Adafruit

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robertk2
 
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7" 800x400 HDMI Backpack with touch no video good LED

Post by robertk2 »

I have two of these units that were purchased at least a year ago (on the back of the display on the bottom they both have 16.22 printed on them which may be a batch number?) and I use them regularly with some UP boards running debian 10 xfce. Recently, we purchased a few more (these have 1921. printed on them) and they don't work with the UP boards, unless I boot the UP board with one of the older displays and then swap one of the new displays. They work fine until I reboot. I also noticed that I can't hotplug any of the displays. They have to be connected when the UP board is turned on.

I'm not very knowledgeable about how these displays are initialized by the BIOS or the Linux Kernel but I assumed it would be by recognizing the TI TFP401A chip on the display (that looks the same on all my displays). The most recent datasheet on the TI website I can find is dated 2016 so maybe I'm wrong about that. The BIOS on the UP board is American Megatrends dated 2020. I tried enabling the Panel Settings in the BIOS to force the HDMI output but that did not work at all.

If anyone could point me in the right direction I would appreciate it.

Best Regards,
R. Koontz

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adafruit_support_mike
 
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Re: 7" 800x400 HDMI Backpack with touch no video good LED

Post by adafruit_support_mike »

You’re right that the computer only sees the TFP401.

I don’t know of any hardware changes that would make a computer fail to recognize a newer version while recognizing an older version.

Try comparing the output from ‘dmesg’ with an older display connected at boot to the output when a newer display is connected. That should at least show what happens during the device recognition process.

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robertk2
 
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Re: 7" 800x400 HDMI Backpack with touch no video good LED

Post by robertk2 »

It's been a while but I wanted to update this. I had to drop this shortly after posting but I was able to pick it back up yesterday. I found that the two older displays have an EDID that is recognized by all my systems. I have a mix of radeon, nvidia, and integrated intel systems. The newer batch of displays do not have a valid EDID. My radeon and nvidia cards call that out in the dmesg report but they handle it and the new displays work. My integrated intel systems do not call out an error in dmesg but when I run xrandr --prop they do recognize the connection as a display and the link status is good but without the EDID info they do not activate the display. With gnome-system-tools installed I can pull open the display GUI and set a resolution but the display stays black. All my intel systems are running Debian 10 and 11 or Mint 19 and 20, with the i915 driver which seems to be the default. I don't know if this would be different on Fedora or SUSE. This is as far as I was able to get and I see three possible solutions. 1. Update the new displays with a valid EDID. I could probably take the EDID from the old displays and write it to the ROM on the new ones. 2. I believe there is another intel driver option and it might handle the lack of EDID like my radeon and nvidia drivers. 3. I believe I could update the xorg.conf files with the display information which should allow X to handle the missing EDID situation.

I'm leaning towards trying to update the EDID on the new displays. I vaguely remember reading something about that around the time I made the original post. If anybody has a better idea I'm willing to listen.

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