iwlwifi for 7260 card: DMA memory allocation fails

[Christian Menard]

Hi everyone,

First of all thanks for the great work on the new release, keep it up!

I'm experimenting with the new iwlwifi driver on a device with 7260 card. I 
enabled support for this card as mentioned in the release notes and added the 
corresponding firmware file iwlwifi-7260-8.ucode. Unfortunately the driver is not 
working out of the box for this card.

The problem breaks down to a failure during DMA memory allocation. Here an 
excerpt from wifi_drv's log:

> Slab too large 131072 reqested 86032 cached 0
> dma alloc 81920 failed
> Slab too large 131072 reqested 105428 cached 0
> dma alloc 101316 failed
> ....
> Slab too large 131072 reqested 86032 cached 0
> dma alloc 81920 failed
> Slab too large 262144 reqested 175072 cached 0
> dma alloc 170960 failed

I naively increased maximum slab size by setting SLAB_STOP_LOG2 in lxc_emul.cc 
to 20. Then failure changes to:

> Failed to get slab for 262144
> dma alloc: 170960 failed

So as it appears such a large slab cannot be allocated. Why is that? What 
would be the right way (tm) to resolve this issue?

Thanks
Christian