[PATCH] modesetting: fail PreInit() if the device has zero connectors

[Tobias Jakobi]

Hello Hans,


Hans de Goede wrote:
> Hi,
> 
> On 20-10-17 19:08, tobias.jakobi1 at uni-bielefeld.de wrote:
>> On laptop systems with a dedicated (powerful) GPU A, you usually
>> have all connectors routed to another (less-powerful) GPU B.
>>
>> With my setup (GPU A = Nvidia, GPU B = Intel) I keep GPU A switched
>> off by not loading the nouveau kernel driver during boot.
>>
>> Loading nouveau while X is running then crashes the server:
>> [   540.775] (EE) 0: /usr/bin/X (xorg_backtrace+0x41) [0x57fa31]
>> [   540.775] (EE) 1: /usr/bin/X (0x400000+0x183429) [0x583429]
>> [   540.775] (EE) 2: /lib64/libpthread.so.0 (0x7ff02d508000+0x10ec0)
>> [0x7ff02d518ec0]
>> [   540.775] (EE) 3: /lib64/libc.so.6 (gsignal+0x38) [0x7ff02d1a2178]
>> [   540.775] (EE) 4: /lib64/libc.so.6 (abort+0x16a) [0x7ff02d1a35fa]
>> [   540.775] (EE) 5: /lib64/libc.so.6 (0x7ff02d16f000+0x2c0b7) [0x7ff02d19b0b7]
>> [   540.775] (EE) 6: /lib64/libc.so.6 (0x7ff02d16f000+0x2c162) [0x7ff02d19b162]
>> [   540.775] (EE) 7: /usr/bin/X (dixRegisterPrivateKey+0x247) [0x452197]
>> [   540.775] (EE) 8: /usr/lib64/xorg/modules/libglamoregl.so
>> (glamor_init+0x160) [0x7ff00ee564d0]
>> [   540.775] (EE) 9: /usr/lib64/xorg/modules/drivers/modesetting_drv.so
>> (0x7ff01c19a000+0x83e1) [0x7ff01c1a23e1]
>> [   540.775] (EE) 10: /usr/bin/X (AddGPUScreen+0xf3) [0x4348b3]
>> [   540.775] (EE) 11: /usr/bin/X (0x400000+0x90271) [0x490271]
>> [   540.775] (EE) 12: /usr/bin/X (0x400000+0x9547b) [0x49547b]
>> [   540.775] (EE) 13: /usr/bin/X (0x400000+0x905d7) [0x4905d7]
>> [   540.775] (EE) 14: /usr/bin/X (xf86VTEnter+0x1bb) [0x47399b]
>> [   540.775] (EE) 15: /usr/bin/X (WakeupHandler+0xda) [0x438e3a]
>> [   540.775] (EE) 16: /usr/bin/X (WaitForSomething+0x1ce) [0x57d6fe]
>> [   540.775] (EE) 17: /usr/bin/X (0x400000+0x34221) [0x434221]
>> [   540.775] (EE) 18: /usr/bin/X (0x400000+0x382f8) [0x4382f8]
>> [   540.775] (EE) 19: /lib64/libc.so.6 (__libc_start_main+0xf0) [0x7ff02d18f670]
>> [   540.776] (EE) 20: /usr/bin/X (_start+0x29) [0x4235b9]
>>
>> In particular note that GLAMOR is initialized for GPU A, which
>> makes no sense since it has no connectors.
>>
>> Fix this by bailing out early in the modesetting DDX when a setup
>> with zero connectors is detected.
>>
>> Signed-off-by: Tobias Jakobi <tjakobi at math.uni-bielefeld.de>
> 
> Sorry, but NACK. The modesetting driver actually had such a check before
> and I removed it because not having a driver breaks rendering on
> the dedicated GPU with "DRI_PRIME=1" for dri2 clients.
sorry, I didn't consider DRI2 in this scenario.


> I guess that there is some sort of assumption in the code for dealing
> with glamor failure that it only happens on coldplug, if you really
> want to be able to modprobe nouveau later you should figure out what
> is exactly going wrong and fix that.
OK, I'll try to get to the bottom of this.


> Note BTW that nouveau should runtime suspend the GPU, even with Xorg
> running and there really is no need to not load nouveau.
No, sadly this is not true on my system. The system has a dual cooling solution,
where cooler A is attached to the CPU, and cooler B to the GPU. When never
inserting nouveau.ko after boot, cooler B stays off the entire time. Once I've
inserted the module, cooler B comes up from time to time _even_ if the GPU is
runtime suspended at that time (and has been since hours).

- Tobias


> 
> Regards,
> 
> Hans