release/5.2.35/powerpc-Ensure-that-swiotlb-buffer-is-allocated-from.patch

From 44bd3df8843ac1e4d1022ecc15df4ccbd2c1489c Mon Sep 17 00:00:00 2001
From: Mike Rapoport <rppt@linux.ibm.com>
Date: Wed, 4 Dec 2019 14:35:24 +0200
Subject: [PATCH] powerpc: Ensure that swiotlb buffer is allocated from low
 memory

commit 8fabc623238e68b3ac63c0dd1657bf86c1fa33af upstream.

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
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>

diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c
index 2eda1ec36f55..99fcdf73f207 100644
--- a/arch/powerpc/mm/mem.c
+++ b/arch/powerpc/mm/mem.c
@@ -270,6 +270,14 @@ 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
 
-- 
2.7.4