Custom EDID with KMS

Kernels & Hardware, configuring network, installing services

Custom EDID with KMS

Postby vol.2 » 2020-05-28 20:10

Hello,

I'm having an issue with KMS getting the wrong video output settings via modedb. I'm using a CGA monitor, so it doesn't have it's own EDID. Setting CEA mode 8 (which is 720x240) works great when I first boot, but as soon as KMS takes over, modedb incorrectly assigns the video output and the monitor drops the signal. From what I understand, modedb is handing off the x,y,vert freq information to some sort of CVT timing calculator which is, in turn, completely making a mess of the video output.
I found some old documentation about creating and inserting a custom EDID in linux in order to solve these kinds of issues. (analog monitors without EDID)

https://wiki.archlinux.org/index.php/Ke ... s_and_EDID

It references this page of linux docs: https://git.kernel.org/pub/scm/linux/ke ... 13756b1075

But this stuff is Arch Linux, and it refers to edid.bin being present in /lib/firmware. I don't see any such files, or anything I would recognize as an EDID file in that location. I also don't know if I can call a custom edid.bin file from boot, or where I would put the command. (cmdline.txt perhaps?)

It's also very important for me to mention here that I am NOT using the X environment, I am operating only from the command line and launching programs from the command line. I'm unaware of whether or not that makes any difference to a potential solution.

Can anyone help me to get my monitor running correctly under KMS?

Thanks,

Brian
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Re: Custom EDID with KMS

Postby Head_on_a_Stick » 2020-05-28 20:50

vol.2 wrote:it refers to edid.bin being present in /lib/firmware. I don't see any such files, or anything I would recognize as an EDID file in that location.

Read the guide again, it explains that you have to either extract or create the file yourself. It also shows how to add it as a kernel command line parameter if you follow the TV Tropes style link.
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Re: Custom EDID with KMS

Postby vol.2 » 2020-05-28 21:22

Head_on_a_Stick wrote:
vol.2 wrote:it refers to edid.bin being present in /lib/firmware. I don't see any such files, or anything I would recognize as an EDID file in that location.



Read the guide again, it explains that you have to either extract or create the file yourself. It also shows how to add it as a kernel command line parameter if you follow the TV Tropes style link.


Ok. Thanks. I will re read.

Just as a sanity check (because I'm a bit of a noob) I would greatly appreciate it if you could answer a couple questions (which are probably obvious to you).

1) Do I have to recompile the kernel to make it work?
2) I add the "kernel command line parameter to cmdline.txt, right?


Thanks,

Brian
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Re: Custom EDID with KMS

Postby Head_on_a_Stick » 2020-05-29 15:41

vol.2 wrote:Do I have to recompile the kernel to make it work?

No.

vol.2 wrote:I add the "kernel command line parameter to cmdline.txt, right?

No. Please click on the link given on the ArchWiki page, I'm not re-typing it here.
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