For the problem when using swiotlb

From: Ding Tianhong
Date: Mon Nov 17 2014 - 06:56:45 EST

Hi Catalin:
The commit 3690951fc6d42f3a0903987677d0e592c49dd8db(arm64: Use swiotlb late initialisation)
switches the DMA mapping code to swiotlb_tlb_late_init_with_default_size(), this will occur a problem
when I run the scsi stress tests, the message as below:

sas_controller swiotlb buffer is full (sz: 65536 bytes)..
DMA: Out of SW-IOMMU space for 65536 bytes at device

The reason is that the swiotlb_tlb_late_init_with_default_size() could only alloc 16M memory for DMA-mapping,
and the param in cmdline "swiotlb=xxx" is useless because the get_free_pages() only use the buddy to assigned a
maximum memory of 16M(The MAX_ORDER is 13 for 4k pages), obviously 16M is too small in many scenes, but
the swiotlb_init() which could reserved a bigger memory as wished could work well for most drivers.

I could not get a better way to fix this problem except to revert this patch, so could you please give me some
advise and help me, thanks very much.


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