[WORKED AROUND] HDMI no connection to /dev/tty? on boot ...

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[WORKED AROUND] HDMI no connection to /dev/tty? on boot ...

Unread postby t.moreau » Wed May 02, 2018 3:42 am

Hi,

This question arises in an effort to use Crux-arm distribution (see bottom of https://crux-arm.nu/Documentation/ReleaseNotes3-3 for root file system image for "generic 64b release") which would be similar to ArchLinux. Maybe the root cause of my difficulty is applicable in other contexts. I did my homework such that the generic complaint "No HDMI for me" is somehow behind me.

The kernel is 3.16.56+, the MicroSD boot partition was established with the ArchLinux image, from which the /boot, /lib/modules and /lib/firmware directories were kept when the Crux root file system image has been un-tarred (neither X11 nor any GUI for now, no Mali GPU usage). Being familiar with the Crux initialization and configuration, I was able to boot and get ssh access.

As I write this, I find an interesting troubleshooting hint, see below.

After the boot, the HDMI output is blank but the HDMI two-way connection is working fine.The HDMI connection is working coherently in the following sense: the EDID information is indeed reflected in

/sys/devices/virtual/amhdmitx/amhdmitx0/edid

and when I change the HDMI parameters, the display (a 7 in. camera monitor sold in the professional video market) indeed reports the change in a temporary pop-up tile (in the otherwise blank screen).

I.e. the HDMI parameter change is effected by

echo -n 480i60hz >/sys/devices/virtual/amhdmitx/amhdmitx0/disp_mode

and then

echo -n 480p60hz >/sys/devices/virtual/amhdmitx/amhdmitx0/disp_mode

(change from 480i to 480p).

After normal boot, the agetty task writes to /dev/tty1 but the screen remains blank.

Things turned OK once I abstained from touching the keyboard for 900 seconds and then hit a key. This is the troubleshooting hint: cat /sys/module/kernel/parameters/consoleblank indeed reports a 900 value.

Then the root cause would be that the kernel boots with a kind-of-console-blank state which is cleared when the console blank timer trigger is reset by a keyboard event. Other Linux distributions for Odroid C2 would have a work-around, while a fix in the kernel would cleanly address the issue for these, mine, and other purposes (e.g. I never saw any boot logo image on the screen but I guess I saw such an image file around a /boot directory).

Regards,

- Thierry
Last edited by t.moreau on Thu May 03, 2018 10:45 am, edited 1 time in total.
t.moreau
 
Posts: 4
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languages_spoken: french, english
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[WORKED AROUND] HDMI no connection to /dev/tty? on boot ...

Unread postby t.moreau » Wed May 02, 2018 2:09 pm

Answering my own question, I had to program a small executable that blanks the console screen and un-blanks it with ioctl codes (merely un-blanking did not work). I inserted a call to this executable in the Crux-specific Linux startup files.

A more elegant solution would be welcome.

In any event, Crux-arm support in Odroid C2 is becoming a reality. It is unfortunate that the Mali drivers are closed source, this being a dis-incentive for X11 support efforts.

Regards,

- Thierry
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t.moreau
 
Posts: 4
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languages_spoken: french, english
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