powerpc: Ensure that swiotlb buffer is allocated from low memory

Some powerpc platforms (e.g. 85xx) limit DMA-able memory way below 4G.
If a system has more physical memory than this limit, the swiotlb
buffer is not addressable because it is allocated from memblock using
top-down mode.

Force memblock to bottom-up mode before calling swiotlb_init() to
ensure that the swiotlb buffer is DMA-able.

Reported-by: Christian Zigotzky <chzigotzky@xenosoft.de>
Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20191204123524.22919-1-rppt@kernel.org

diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c
index 9488b63..617c277 100644 (file)
--- a/arch/powerpc/mm/mem.c
+++ b/arch/powerpc/mm/mem.c
@@ -289,6 +289,14 @@ void __init mem_init(void)
        BUILD_BUG_ON(MMU_PAGE_COUNT > 16);
 
 #ifdef CONFIG_SWIOTLB
+       /*
+        * Some platforms (e.g. 85xx) limit DMA-able memory way below
+        * 4G. We force memblock to bottom-up mode to ensure that the
+        * memory allocated in swiotlb_init() is DMA-able.
+        * As it's the last memblock allocation, no need to reset it
+        * back to to-down.
+        */
+       memblock_set_bottom_up(true);
        swiotlb_init(0);
 #endif