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

[Tim Gardner]

On 01/22/2016 07:56 AM, Mark wrote:
> 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
>
>
>

In the event that upstream does not come up with a solution, how about 
if we leave ZONE_DMA enabled in the low-latency flavour ? After all, it 
seems most of the devices that this affects are audio related (except 
for the parallel port).

rtg
-- 
Tim Gardner tim.gardner at canonical.com