[PATCH kernel] powerpc/powernv/ioda2: Gracefully fail if too many TCE levels requested

[Gavin Shan]

On Wed, Feb 22, 2017 at 03:43:59PM +1100, Alexey Kardashevskiy wrote:
>The IODA2 specification says that a 64 DMA address cannot use top 4 bits
>(3 are reserved and one is a "TVE select"); bottom page_shift bits
>cannot be used for multilevel table addressing either.
>
>The existing IODA2 table allocation code aligns the minimum TCE table
>size to PAGE_SIZE so in the case of 64K system pages and 4K IOMMU pages,
>we have 64-4-12=48 bits. Since 64K page stores 8192 TCEs, i.e. needs
>13 bits, the maximum number of levels is 48/13 = 3 so we physically
>cannot address more and EEH happens on DMA accesses.
>
>This adds a check that too many levels were requested.
>
>It is still possible to have 5 levels in the case of 4K system page size.
>
>Signed-off-by: Alexey Kardashevskiy <aik at ozlabs.ru>
>---

Acked-by: Gavin Shan <gwshan at linux.vnet.ibm.com>