Bug 94803

Summary: nouveau bug crashes kernel 4.4.6 on warm boot
Product: xorg Reporter: Michael Daum <mic.daum>
Component: Driver/nouveauAssignee: Nouveau Project <nouveau>
Status: NEW --- QA Contact: Xorg Project Team <xorg-team>
Severity: normal    
Priority: medium    
Version: unspecified   
Hardware: Other   
OS: All   
i915 platform: i915 features:
Description Flags
picture from stack trace taken with camera
dump of the nv50_disp_intr_supervisor function none

Description Michael Daum 2016-04-02 23:14:46 UTC
Created attachment 122684 [details]
picture from stack trace taken with camera

Whenever doing a warm boot (reboot), kernel 4.4.6 crashes showing the stack trace in the attached picture. The kernel boots fine when doing a cold start or after pressing the reset button.

The GPU in question is a "PNY Quadro FX 580" (Tesla / G96) with two attached monitors, both connected on display port.

The crash happens quite early when the kernel sets mode on the framebuffer. Resolution is set to 1920x1200 px, 240x75 cols/lines.


picture of the screen showing the stack trace
dump of "nv50_disp_intr_supervisor" function from the 4.4.6 vmlinux
Comment 1 Michael Daum 2016-04-02 23:16:41 UTC
Created attachment 122685 [details]
dump of the nv50_disp_intr_supervisor function
Comment 2 Ilia Mirkin 2016-04-02 23:36:31 UTC
0x80c (2060) looks like this:

   0xffffffff814daf32 <+2050>:	xor    %edx,%edx
   0xffffffff814daf34 <+2052>:	mov    %rax,%rdi
   0xffffffff814daf37 <+2055>:	mov    $0xc,%eax
   0xffffffff814daf3c <+2060>:	divl   -0x88(%rbp)

which has gotta come from

nv50_disp_intr_unk20_2_dp(...) {

	u32 dpctrl = nvkm_rd32(device, 0x61c10c + loff);
	link_nr = hweight32(dpctrl & 0x000f0000);


 	value = value - (3 * !!(dpctrl & 0x00004000)) - (12 / link_nr);

Which means that on boot link_nr is 0. Michael, if you're up for some kernel patching, can you just add a

if (!link_nr) {
  nvkm_error(subdev, "link_nr = 0; dpctrl: %08x\n", dpctrl);

right after the link_nr assignment in that function?
Comment 3 Michael Daum 2016-04-03 01:11:49 UTC
The patch from Ilia prevents the kernel from crashing. Reboot does not fail any longer. Additionally _most_ of the time both monitors come up at reboot.

But on some reboots one of the monitors stays black and the kernel logs following error (from dmesg):

[    0.955154] nouveau 0000:01:00.0: disp: outp 04:0006:0384: link training failed
[    0.973972] nouveau 0000:01:00.0: disp: outp 04:0006:0384: link training failed
[    0.974279] nouveau 0000:01:00.0: disp: link_nr = 0; dpctrl: 00401101

The value of dpctrl is always the same (00401101) then.

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