[PATCH 3/4] arm64: Default to 32-bit ZONE_DMA

Nicolas Saenz Julienne
2020-10-01T16:18:04Z

The Raspberry Pi 4 needs two DMA zones as some of its devices can only
DMA into the 30-bit physical address space. We solved that by creating
an extra ZONE_DMA covering the 30-bit. It turns out that creating extra
zones unnecessarily broke Kdump on large systems. So default to a single
32-bit wide ZONE_DMA and only define both zones if running on RPi4.

Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
---
arch/arm64/mm/init.c | 12 ++++++++----
1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
index e1a69a618832..3c3f462466eb 100644
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c
@@ -43,8 +43,6 @@
#include <asm/tlb.h>
#include <asm/alternative.h>

-#define ARM64_ZONE_DMA_BITS 30
-
/*
* We need to be able to catch inadvertent references to memstart_addr
* that occur (potentially in generic code) before arm64_memblock_init()
@@ -388,8 +386,14 @@ void __init arm64_memblock_init(void)
early_init_fdt_scan_reserved_mem();

if (IS_ENABLED(CONFIG_ZONE_DMA)) {
- zone_dma_bits = ARM64_ZONE_DMA_BITS;
- arm64_dma_phys_limit = max_zone_phys(ARM64_ZONE_DMA_BITS);
+ /*
+ * early_init_dt_scan() might alter zone_dma_bits based on the
+ * device's DT. Otherwise, have it cover the 32-bit address
+ * space.
+ */
+ if (zone_dma_bits == ZONE_DMA_BITS_DEFAULT)
+ zone_dma_bits = 32;
+ arm64_dma_phys_limit = max_zone_phys(zone_dma_bits);
}

if (IS_ENABLED(CONFIG_ZONE_DMA32))
--
2.28.0