While trying to fix another bug I tried using kernel v4.0 and noticed that after X.org has started (running fluxbox with mythtv in my case) the screen stays black. My screen is attached on HDMI. During boot I can see the console output just fine but when X started it stays black. I don't even see the first small X shaped cursor. I bisected this back to commit 0ea5fe8a83c2 ("drm/nouveau/kms: default to panel scaling, except for fixed panels prior to nv50"). From the commit message I suspect that "panel scaling" (whatever that means) does not work on my NVAA. I check the values of nv_connector->type and nv_connector->scaling_mode on both the bisected commit and the parent (last commit working). The type is 0x61 (DCB_CONNECTOR_HDMI_1) in both cases and the scaling_mode is 0 (DRM_MODE_SCALE_NONE) when the screen stays black while it is 1 (DRM_MODE_SCALE_FULLSCREEN) when everything works normally. dmesg doesn't show anything interesting though. Maybe a higher log level, please give me some hints which component and which debug level you may need.
Created attachment 115722 [details] xrandr --verbose from 3.19 kernel
Created attachment 115723 [details] xrandr --verbose from 4.0 kernel
Created attachment 115724 [details] Xorg log from 4.0 kernel
Apparently this is due a custom modesetting I needed to use before attaching a AV receiver. My TV required a custom modesetting with resolution 1360x768, but this is not supported by the AV receiver. So when using the unsupported resolution with panel scaling nothing is displayed. In my case I could remove the custom modesetting as the AV receiver has a proper EDID with 1920x1080 (which is scaled down by that box for the TV). If someone needs a custom modesetting the old fullscreen scaling should be used, e.g. xrandr --output HDMI-1 --prop 'scaling mode' 'Full'
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