[Letux-kernel] LX16 SPI Display

[H. Nikolaus Schaller]

> Am 14.01.2025 um 17:12 schrieb H. Nikolaus Schaller <hns at goldelico.com>:
> 
> root at letux:~# ./fbpng 1280x720_board.png
> 1280x720_board.png: 1280x720 @ 24bpp
> ioctl(FBIOPUT_VSCREENINFO): Invalid argument
> Bus error
> root at letux:~# 
> 
> The Bus error is because there is no exit in error case. But the ioctl is still defined.

Ok, the most likely reason might be that I do not have the correct UAPI headers on the LX16
and struct fb_var_screeninfo fbvar; is defined differently.

Indeed there is /usr/include/linux/fb.h and /include/linux/fb.h
But the diff is only #include <linux/vesa.h> vs. #define VESA* and a comment.

There is another potential error path in the ioctl() if the code is good but the image too large...
(fbcon_modechange_possible() or fb_set_var() or fbcon_update_vcs() may all fail)
https://elixir.bootlin.com/linux/v6.13-rc3/source/drivers/video/fbdev/core/fb_chrdev.c#L81

So I tried with a smaller PNG... Nope...

root at letux:~# ./fbpng picts_32.png 
picts_32.png: 32x32 @ 24bpp
ioctl(FBIOPUT_VSCREENINFO): Invalid argument
Bus error
root at letux:~# 

It might as well be that 24bpp isn't accepted...

root at letux:~# fbset 

mode "480x320"
    geometry 480 320 480 320 16
    timings 0 0 0 0 0 0 0
    rgba 5/11,6/5,5/0,0/0
endmode

root at letux:~# 

The display is not 24bpp and Xorg might be more generous than all
these direct fb access tools.

New ideas welcome...

BR,
Nikolaus