[Bug 89360] [bdw-u iommu] DMAR error -> GPU hang

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=89360

--- Comment #59 from Du, Changbin <changbin.du at intel.com> ---
(In reply to Du, Changbin from comment #58)
> --- a/drivers/iommu/intel-iommu.c
> +++ b/drivers/iommu/intel-iommu.c
> @@ -3787,7 +3787,7 @@ static void intel_unmap(struct device *dev, dma_addr_t
> dev_addr, size_t size)
>  	struct intel_iommu *iommu;
>  	struct page *freelist;
>  
> -	if (iommu_no_mapping(dev))
> +	//if (iommu_no_mapping(dev))
>  		return;
>

Our QA helped verify on both Nuc and Server paltofrms, the the result is
intersting:
1. for server Iris Pro 6200 (Broadwell GT3e), we still can reporudce it w/
above change.
2. for NUC HD Graphics 5500 (Broadwell GT2), didn't see DMAR error w/ above
change.

GT3e has 128MB eDRAM, while GT2 doesn’t. So probably there is problem in gfx
cache or memory.

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