Re: drm: simpledrm: fbdev emulation error with CONFIG_DRM_SIMPLEDRM enabled

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Hi,

Did anything happen with this issue? I've updated linux kernel to 5.14.7 from 5.13 today, and I've been hit with a very similar problem (even inside qemu), except in my case the height reported in "bad framebuffer height" was twice the actual height, not three times. After some digging around I've figured out that at the end of drm_fb_helper_single_fb_probe, surface_height is multiplied by CONFIG_DRM_FBDEV_OVERALLOC/100, which was somewhy set to 200 in my kernel config. Setting it to 100 fixed that problem. (It looks like the default now, I don't know why was it set to 200 in my config, maybe the old default was different).

However it's still very buggy, even after setting CONFIG_DRM_FBDEV_OVERALLOC to 100. On my notebook (ASUS G551JW, with a 4th gen i7 cpu), this is what I observe: * after the kernel boots, the tux logos rapidly flicker at the top of the screen and I only see text at the bottom of the screen. After a few seconds it returns to normal. * when starting X, whet it switches to a new VT the tux logos reappear along with some text, but only in the upper left corner. This is also only happens for a second or so, until X overtakes the display. * when terminating X, the tux logos with the garbage text remain in the upper left corner, but the rest of the screen is replaced with the correct contents. The garbage in the top left corner remains until something overwrites it (like scrolling the terminal). So it works, but buggy as hell and at this point I'm better disabling simpledrm and just relying on the i915 driver, losing early console. I tried booting with drm.debug=0x1ff, but by the time I could run dmesg it generated so many messages that the early boot messages were already lost.

Now, my desktop is even worse. Motherboard is an ASRock Z87M Extreme4, with a GeForce GT 640 and GTX 980 cards (the integrated GPU in the intel CPU is disabled in UEFI settings). Unfortunately this requires the proprietary nvidia drivers, so it's probably my own problem, but anyway it works until I it loads the nvidia drivers, then afterwards (while still in fbcon) I instead get 4 or 5 small copies of my terminal in the upper part of the screen with wrong stride, so it's completely unreadable. And if I ever start X, I won't have any fbcon until reboot. So 5.14 is basically unusable on this machine.

Any ideas what should I try? Everything worked well with 5.13 and its simplefb.

Thanks,
Zoltan




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