[PATCH] powerpc: ensure that swiotlb buffer is allocated from low memory

[Mike Rapoport]

From: Mike Rapoport <rppt@xxxxxxxxxxxxx>

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.

Link: https://lkml.kernel.org/r/F1EBB706-73DF-430E-9020-C214EC8ED5DA@xxxxxxxxxxx
Reported-by: Christian Zigotzky <chzigotzky@xxxxxxxxxxx>
Signed-off-by: Mike Rapoport <rppt@xxxxxxxxxxxxx>
Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Cc: Darren Stevens <darren@xxxxxxxxxxxxxxxx>
Cc: mad skateman <madskateman@xxxxxxxxx>
Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Cc: Nicolas Saenz Julienne <nsaenzjulienne@xxxxxxx>
Cc: Paul Mackerras <paulus@xxxxxxxxx>
Cc: Robin Murphy <robin.murphy@xxxxxxx>
Cc: Rob Herring <robh+dt@xxxxxxxxxx>
---
 arch/powerpc/mm/mem.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c
index be941d382c8d..14c2c53e3f9e 100644
--- a/arch/powerpc/mm/mem.c
+++ b/arch/powerpc/mm/mem.c
@@ -260,6 +260,14 @@ 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
 
-- 
2.24.0