powerpc/dma: Fix invalid DMA mmap behavior
The refactor of powerpc DMA functions in commit 6666cc17 ("powerpc/dma: remove dma_nommu_mmap_coherent") incorrectly changes the way DMA mappings are handled on powerpc. Since this change, all mapped pages are marked as cache-inhibited through the default implementation of arch_dma_mmap_pgprot. This differs from the previous behavior of only marking pages in noncoherent mappings as cache-inhibited and has resulted in sporadic system crashes in certain hardware configurations and workloads (see Bugzilla). This commit restores the previous correct behavior by providing an implementation of arch_dma_mmap_pgprot that only marks pages in noncoherent mappings as cache-inhibited. As this behavior should be universal for all powerpc platforms a new file, dma-generic.c, was created to store it. Fixes: 6666cc17 ("powerpc/dma: remove dma_nommu_mmap_coherent") # NOTE: fixes commit 6666cc17 released in v5.1. # Consider a stable tag: # Cc: stable@vger.kernel.org # v5.1+ # NOTE: fixes commit 6666cc17 released in v5.1. # Consider a stable tag: # Cc: stable@vger.kernel.org # v5.1+ Cc: stable@vger.kernel.org # v5.1+ Signed-off-by: Shawn Anastasio <shawn@anastas.io> Reviewed-by: Alexey Kardashevskiy <aik@ozlabs.ru> Reviewed-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/20190717235437.12908-1-shawn@anastas.io
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