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[Ming Lei <1386490@xxxxxxxxxxxxxxxxxx>]

>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?

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

Status in “linux” package in Ubuntu:
  Confirmed
Status in “linux” source package in Utopic:
  Confirmed
Status in “linux” source package in Vivid:
  Confirmed

Bug description:
  Starting in 3.15, arm64 began defaulting to non-coherent dma_ops:

  commit c7a4a7658d689f664050c45493d79adf053f226e
  Author: Ritesh Harjani <ritesh.harjani@xxxxxxxxx>
  Date:   Wed Apr 23 06:29:46 2014 +0100

      arm64: Make default dma_ops to be noncoherent

  Firmware (dtb in the case of the m400) is responsible for telling the
  kernel when a device requires coherent dma_ops. However, as of utopic,
  this property is not being inherited by downstream devices.
  Specifically, the xgene-pcie device is marked as coherent, but the
  devices behind it (mellanox card) still get initialized with non-
  coherent ops.

  This results in the mlx4 driver bailing out with the following messages:
  [   18.703635] mlx4_core 0000:01:00.0: command 0x23 timed out (go bit not cleared)
  [   18.710911] mlx4_core 0000:01:00.0: Failed to initialize queue pair table, aborting

  
  There's an upstream discussion on the topic here:
    http://www.spinics.net/lists/arm-kernel/msg362320.html

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