HDMI doesn't work with projector that doesn't support EDID

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HDMI doesn't work with projector that doesn't support EDID

Postby Alex230-WR » Mon Dec 01, 2014 3:11 pm

I have a problem with connecting Wandboard to the projector that use TFP401A video chip. That video chip doesn't send EDID data. Projector works normally with Android-x86 on PC, and it works with u-boot logo on Wandboard, but there is no video at all when I boot to Android or Ubuntu (official images from wandboard.org). When I connect the projector to Wandboard, Ubuntu shows messages on dmesg:
mxc_hdmi: Read EDID again
mxc_hdmi: No modes read from edid
mxc_hdmi: create default modelist
And there is no video on projector. But when I connect a monitor, I see the same messages, and monitor works normally.
Android display another message on dmesg:
mxc_hdmi mxc_hdmi: same edid
both with monitor (when video works) and with projector (when video doesn't work).
I think there is a bug in iMX6 kernel (strings "same edid" and "create default modelist" are in file drivers/video/mxc_hdmi.c), and I want to fix it. Can you point me to any patches or instructions, or working kernel sources that work normally with absent EDID?
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Re: HDMI doesn't work with projector that doesn't support EDID

Postby Alex230-WR » Fri Dec 05, 2014 2:03 pm

Problem is solved, it was because of defective HDMI cable that didn't transmit EDID data. However, it's strange that Linux and Android on PC and U-boot on Wandboard work even without EDID, but Linux and Android on Wandboard don't work. It's probably related to HDMI driver for iMX6 in kernel.
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Re: HDMI doesn't work with projector that doesn't support EDID

Postby JayminD » Fri Dec 05, 2014 2:18 pm

Hello Alex,

for your problem I would suggest to below link, its may help you to solve your query. :!:

http://forums.wandboard.org/viewtopic.php?f=3&t=733&sid=c635783b9598becb04cc899f4098d4a7

and one more thing is that, there is some issue with I2C and HDMI in wandboard.

Regards
Jaymin D
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Re: HDMI doesn't work with projector that doesn't support ED

Postby arham » Wed Jan 28, 2015 9:26 am

Thanks for the responses. I *am* already using ext4. And as I wrote I already tried three different cards (all three even different models). How would trying *another* card give any insight?
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Re: HDMI doesn't work with projector that doesn't support ED

Postby Tapani » Wed Jan 28, 2015 10:35 am

The iMX6 HDMI driver needs to read an EDID. This is a pain.

The splash screen in u-boot is a hack: using LVDS output with very hard coded timings (not guaranteed to work).
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Re: HDMI doesn't work with projector that doesn't support ED

Postby Captain » Thu Oct 22, 2015 7:29 pm

Tapani wrote:The iMX6 HDMI driver needs to read an EDID. This is a pain.

Hmm ... yes, this is a pain.

I just got my Wandboard Quad - great board, BTW! This is the first problem I encountered. I have a DVI monitor, and am using an HDMI to DVI cable. I can see the boot process over the serial port, and the Wandboard splash screen momentarily before the monitor goes dark.

The splash screen in u-boot is a hack: using LVDS output with very hard coded timings (not guaranteed to work).


I'm new to this, and am no video expert. Forgive me if these questions seem simple, but ... would it be possible to modify the driver such that the EDID isn't required? Or could the splash screen hack be implemented permanently? You say the hack isn't guaranteed to work, but it obviously works for me! :)

Thanks!

-- Captain
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Re: HDMI doesn't work with projector that doesn't support ED

Postby blue_z » Thu Oct 22, 2015 7:57 pm

Captain wrote:You say the hack isn't guaranteed to work, but it obviously works for me!
It's a low resolution which most monitors and TVs can handle.

Captain wrote:would it be possible to modify the driver such that the EDID isn't required?
That would mean you would be hardcoding a video mode to use. That can be dangerous.

There's a scheme to provide an EDID through the kernel command line, but the i.MX6 HDMI driver hasn't been updated to have that capability (the last time I checked).

FWIW I did a patch to the driver so that a Sony widescreen CRT TV could be used as a Wandboard display. If the read of the EDID fails, then the driver uses a built-in default EDID, which happens to be my Sony's EDID (that a PC can read but the Wandboard cannot).


Regards
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Re: HDMI doesn't work with projector that doesn't support ED

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Re: HDMI doesn't work with projector that doesn't support ED

Postby RobinsBright2 » Fri Sep 29, 2017 7:09 am

Projectors usually come with fixed resolutions, meaning regardless of the quality of the signal they receive, they can only output in one resolution. Here's an example: a XGA (1024 x 768) projector that receives an HD (1920 x 1080) signal must shrink the information so it outputs in the 1024 x 768 format. projector price in pakistan
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