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Generic debugging steps

Changing the panning

Some devices might have a framebuffer virtual size thats twice as big as the panel resolution, this is a common double buffering method. The application renders to one side of the display while the panning is set to the other side. You can try changing the panning with the `panning` file in the sysfs directory.

$ cat /sys/class/graphics/fb0/virtual_size
todo: add file contents here
$ cat /sys/class/graphics/fb0/pan
todo: add file contents here
$ echo 0 0 > /sys/class/graphics/fb0/pan

Qualcomm framebuffer (mdss, mdp3)

MSM framebuffer doesn't work

We found out that removing the 3D driver support makes the MSM framebuffer work. See #66.


-> Device Drivers                                                                                                                                           │  
    -> Graphics support
        -> MSM 3D Graphics driver

On devices using the mdss_fb driver, adding mdss-fb-init-hack to the dependencies of the device package (example) might help.

Screen output flicker and inactivity

If you notice a very brief flicker upon boot, but immediately disappears and screen turns black, you might have a buggy framebuffer Qualcomm MDSS MDP3 driver.

You can try patching the source code by removing the function assigned to the mdp3_interface->off_fnc in the mdp3_ctrl.c file.

See example patch: 05_fix_mdp3_ctrl_off.patch

Screen output messed up

If the output on the screen is not aligned correctly (see picture) it's probably because you have a wrong value in /sys/class/graphics/fb0/bits_per_pixel.

You can try patching the source code by setting a different video mode (RGB/ARGB/RGBA/YCRYCB/...).

This may also help, when your X11 is segfaulting (see #779).

See example patch: 06_fix_mdss_fb_rgb_mode.patch

My screen is red!

Patch your kernel to report the right framebuffer information, for example with the following patch. If you have successfully patched your kernel that way, please edit this page and link to the merge request below (so we get a few more examples).

diff --git a/drivers/video/msm/mdss/mdss_fb.c b/drivers/video/msm/mdss/mdss_fb.c
index 53112ca6..69673017 100644
--- a/drivers/video/msm/mdss/mdss_fb.c
+++ b/drivers/video/msm/mdss/mdss_fb.c
@@ -569,7 +569,7 @@ static int mdss_fb_probe(struct platform_device *pdev)
 	mfd->bl_level = 0;
 	mfd->bl_scale = 1024;
	mfd->bl_min_lvl = 30;
-	mfd->fb_imgType = MDP_RGBA_8888;
+	mfd->fb_imgType = MDP_RGB_888;
 	mfd->pdev = pdev;
 	if (pdata->next)

Alternative patch: 0001-fix-video-argb-setting.patch (requires CONFIG_FB_MSM_DEFAULT_DEPTH_ARGB8888=y in the kernel config).

A workaround might be setting the default color depth to 16 bits per pixel (see this comment).

See also

  • pmaports#211 framebuffer: red and blue are swapped on devices using MSM8974 (resolved)

Screen doesn't refresh

Check if your screen refreshes when you do the following:

$ cat /sys/class/graphics/fb0/modes > /sys/class/graphics/fb0/mode

If it does, add msm-fb-refresher to the depends= of your device-package. It will basically do the same automatically.

(If the above command does not refresh your screen, you could try the msm-fb-refresher anyway.)

Make sure you zap the device rootfs after enabling the msm refresher, otherwise it will only get installed as a service and not enabled by the postmarketos-base install script (you'll only see a second of splash-screen otherwise and the refresher won't be restarted after exiting the initramfs

Screen is blank outside of Weston

Something like that should help, see #603:

$ echo 0 > /sys/class/graphics/fb0/blank
$ echo 1 > /sys/devices/fd900000.qcom,mdss_mdp/qcom,mdss_fb_primary.134/leds/lcd-backlight/brightness

Debugging the kernel driver

If you have some time to spend on getting your video driver working right, consider adding printk statements in your kernel to understand what it does and where it fails. After building your kernel and flashing, check dmesg for your debug output. See #1618 (comment) for a detailed example.

See also

  • pmaports#211: framebuffer: red and blue are swapped on devices using MSM8974
  • pmaports#297: Alternative patch to fix refresh rate for kernel 3.4.113 android_kernel_oppo_msm8974 and similar