[PATCH Xenial 4.4] UBUNTU: [Config] CONFIG_ZONE_DEVICE=y for amd64

[Mark]

On Tue Jan 5 15:00:58 UTC 2016, Tim Gardner wrote:

>In order for ZONE_DEVICE to be enabled for amd64 you have to set
ZONE_DMA=n (which is a change
>from our current annotation policy). In effect, this precludes devices
that can only DMA from
>memory addresses below 16MB. Does anyone think this is a bad idea ?
ZONE_DEVICE is a prequisite
>for supporting NVDIMM devices which I believe we'll start seeing more of
in the near future.

This change breaks PC parallel port DMA and will affect other ISA & PCMCIA
devices too I guess.

https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1536813
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1534647
https://bugzilla.kernel.org/show_bug.cgi?id=110931

Best solution would be to get upstream to not break ZONE_DMA of course.
>From the commit message
(https://lists.01.org/pipermail/linux-nvdimm/2015-August/001810.html):
"However, since we have run out of ZONES_SHIFT bits this functionality
currently depends on sacrificing ZONE_DMA."

If that isn't feasible, I'd suggest not shipping the default kernel with
ZONE_DEVICE, but perhaps make it available in a PPA for those that
want/need it.


Mark