[Nouveau] Fwd: videowall

[Stéphane Marchesin]

On Sat, Feb 1, 2014 at 9:45 AM, Christian Stöveken <
christian.stoeveken at gmail.com> wrote:

> On Fri, Jan 31, 2014 at 11:25 AM, Dave Airlie <airlied at gmail.com> wrote:
>>
>>
>> You'll probably run out of PCI address space with too many cards,
>>
>> Dave.
>>
>
> That could possibly happen - I don't know how to check though.
>
> Looks like the ID's are fine to me.
>
> Could CONFIG_VGA_ARB_MAX_GPUS (is set to 16) be the problem?
>

This problem happens way before the kernel starts. When the bios sets up
the pci resource space, you have something between 512M and 2GB available
for pci resources (this depends on the bios). Each card will usually eat
128M or 256M of pci resource space (although it depends on the cards) so
it's possible to run out. When that happens, some bioses won't boot, others
will just disable some devices. You can look for that info in your kernel
logs, the e820 area size is printed (look for something like e820: [mem
0xd0000000-0xffefffff] available for PCI devices). You can use lspci -v to
check if all the cards come up with their pci resources and how things fit
in there. If all of them have a pci resource then you're fine on that front.

Stéphane
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