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With recent changes that introduced support for Page Pool in stmmac, Jon
reported that NFS boot was no longer working on an ARM64 based platform
that had the IP behind an IOMMU.

As Page Pool API does not guarantee DMA syncing because of the use of
DMA_ATTR_SKIP_CPU_SYNC flag, we have to explicit sync the whole buffer upon
re-allocation because we are always re-using same pages.

In fact, ARM64 code invalidates the DMA area upon two situations [1]:
	- sync_single_for_cpu(): Invalidates if direction != DMA_TO_DEVICE
	- sync_single_for_device(): Invalidates if direction == DMA_FROM_DEVICE

So, as we must invalidate both the current RX buffer and the newly allocated
buffer we propose this fix.

[1] arch/arm64/mm/cache.S
Reported-by: Jon Hunter <jonathanh@nvidia.com>
Tested-by: Jon Hunter <jonathanh@nvidia.com>
Fixes: 2af6106a

 ("net: stmmac: Introducing support for Page Pool")
Signed-off-by: Jose Abreu <joabreu@synopsys.com>
Tested-by: Ezequiel Garcia <ezequiel@collabora.com>
Signed-off-by: David S. Miller <davem@davemloft.net>