Comment 4 for bug 1386490

On Thu, Nov 27, 2014 at 8:17 PM, Ming Lei <email address hidden> wrote:
> >From ARM64 maintainer's viewpoint:
>
> http://marc.info/?l=linux-arm-kernel&m=141708838404470&w=2
>
> Either way, I don't think it's a problem for the kernel. We just need to
> change the default DMA ops to coherent when booting with ACPI (using
> non-coherent ops for a coherent device is not safe as the CPU can
> corrupt cache lines written by the device).
>
> So I suggest to revert c7a4a7658d689f6 for utopic since utopic ships APM's
> non-upstreamed PCI implementation, and APM's ARM64 Soc is coherent
> arch.
>
> Dann, what do you think about it?

Ming,
 Thanks for looking into this.
I'm not sure I follow the relevancy of a couple things:

 - The upstream discussion seems to have gotten rerouted to solving
the problem for ACPI, but this issue is regarding device-tree (as was
your patch), since that is what Ubuntu/m400 uses. I'm having trouble
seeing how the ACPI solution helps us.

 - I'm confident I reproduced this problem with all upstream bits
after PCI was merged. Therefore my assumption was that this issue is
independent of PCI stack choice. Do you believe that the solution for
the upstream PCI stack is different than the solution for the APM PCI
stack?

In general I'm OK with a revert of c7a4a7658d689f6 for utopic, as long
as we have a plan for an upstream answer for vivid and beyond (>=
3.19). I don't think the kernel team would support a plan that
involves carrying this revert indefinitely (if that's what you're
suggesting, I'm not sure it is).

  -dann

> Thanks,
>
> ** Changed in: linux (Ubuntu Utopic)
> Assignee: (unassigned) => Ming Lei (tom-leiming)
>
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> https://bugs.launchpad.net/bugs/1386490
>
> Title:
> HP ProLiant m400 nic doesn't work after trusty
>
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