X cannot use /dev/fb1

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X cannot use /dev/fb1

Postby keithspg » Sun Feb 28, 2021 1:09 am

This used to work. Last time I checked was under kernel 5.4.x. I just checked it again, tonight and it does not seem to actually direct any graphic output to /dev/fb1.

I have a 3.5" spi tft touch screen. I put a "fbcon=map:10" in the /boot/cmdline.txt and put
$this->bbcode_second_pass_code('', '# PItft 3.5" screen
dtparam=spi=on
dtoverlay=pitft35-resistive,rotate=90,speed=32000000,fps=20')
into /boot/config.txt and when it boots, I get a console. If I set up fbturbo with a config:

$this->bbcode_second_pass_code('', 'Section "Device"
Identifier "Allwinner A10/A13 FBDEV"
Driver "fbturbo"
Option "fbdev" "/dev/fb1"
Option "SwapbuffersWait" "true"
EndSection')

and start X, it displays on the HDMI (/dev/fd0?). If I change it to /dev/fb0, it still goes to the HDMI. It is as if xorg is ignoring my directive to /dev/fb1. When I do have this set and start X, the console does go numb and I cannot type anything on the cli but no graphic X window is ever displayed. I have tried using the regular fbdev driver as well and get the same result. Is there some cmdline.txt directive that needs to be put in to enable this?
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Re: X cannot use /dev/fb1

Postby keithspg » Sun Feb 28, 2021 4:05 pm

So, I tried a number of things and get the same result:
1) Went back to a 5.4.x kernel
2) Tried downgrading xorg-server and xorg-server-common from 1.20.10 to 1.20.9.
3) Tried different timings for my display (pitft35-resistive) went down to 16mhz and 10 fps from 32/20.
same result. The screen flashes black then when it returns it has no cursor and just displays the console. I cannot type anything in it. If I stop X, the console returns functionality and the blinking cursor returns.

I Compared the xorg logs between the HDMI successful launch of X and the failed launch on the SPI display and cannot see much of anything. X looks like it is happily running, I just cannot see it on the SPI display. If the HDMI is plugged in at boot, it shows what is supposed to be showing on the spi display. The only interesting line from the xorg log is this:
Successful HDMI launch
$this->bbcode_second_pass_code('', 'Kernel command line: coherent_pool=1M 8250.nr_uarts=0 snd_bcm2835.enable_compat_alsa=0 snd_bcm2835.enable_hdmi=1 bcm2708_fb.fbwidth=1824 bcm2708_fb.fbheight=984 bcm2708_fb.fbdepth=16 bcm270>')
Unsuccessful SPI display launch
$this->bbcode_second_pass_code('', 'Kernel command line: coherent_pool=1M 8250.nr_uarts=0 snd_bcm2835.enable_compat_alsa=0 snd_bcm2835.enable_hdmi=1 bcm2708_fb.fbwidth=656 bcm2708_fb.fbheight=416 bcm2708_fb.fbdepth=16 bcm2708>')

so, it looks like it is sending it to the small display, but nothing shows.
Any pointers as to how I might get the display back on my little spi screen?
keithspg
 
Posts: 221
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Re: X cannot use /dev/fb1

Postby graysky » Sun Feb 28, 2021 5:28 pm

You might be move coverage posting to the RPi forums...
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Re: X cannot use /dev/fb1

Postby keithspg » Sat Mar 13, 2021 4:38 am

this is really strange and I believe it is a driver problem with the dtoverlay I am using
$this->bbcode_second_pass_code('', 'dtoverlay=pitft35-resistive')
I can get a login prompt on it and can even launch weston from it and get weston to display graphics on it, but cannot get fbdev to actually direct output to the screen under xorg.
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