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 <[email protected]> Signed-off-by: Mike Rapoport <[email protected]> Reviewed-by: Christoph Hellwig <[email protected]> Signed-off-by: Michael Ellerman <[email protected]> Link: https://lore.kernel.org/r/[email protected]
zandrey · Dec 13, 2019 · 8fabc62 · 8fabc62
1 parent 656c21d
commit 8fabc62
Showing 1 changed file with 8 additions and 0 deletions.
diff --git 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