[PATCH 2/2] ARM: Clamp MAX_DMA_ADDRESS to 32-bit

[Florian Fainelli <f.fainelli@gmail.com>]

MAX_DMA_ADDRESS is a virtual address, therefore it needs to fit within a
32-bit unsigned quantity. Platforms defining a DMA zone size in
their machine descriptor can easily overflow this quantity depending on
the DMA zone size and/or the PAGE_OFFSET setting.

In most cases this is harmless, however in the case of a
CONFIG_DEBUG_VIRTUAL enabled, __virt_addr_valid() will be unable to
return that MAX_DMA_ADDRESS is valid because the value passed to that
function is an unsigned long which has already overflowed.

Fixes: e377cd8221eb ("ARM: 8640/1: Add support for CONFIG_DEBUG_VIRTUAL")
Fixes: 2fb3ec5c9503 ("ARM: Replace platform definition of ISA_DMA_THRESHOLD/MAX_DMA_ADDRESS")
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
---
 arch/arm/include/asm/dma.h | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/arm/include/asm/dma.h b/arch/arm/include/asm/dma.h
index f244ee68e814..ea47420babd4 100644
--- a/arch/arm/include/asm/dma.h
+++ b/arch/arm/include/asm/dma.h
@@ -8,10 +8,12 @@
 #ifndef CONFIG_ZONE_DMA
 #define MAX_DMA_ADDRESS	0xffffffffUL
 #else
+#include <linux/minmax.h>
 #define MAX_DMA_ADDRESS	({ \
 	extern phys_addr_t arm_dma_zone_size; \
 	arm_dma_zone_size && arm_dma_zone_size < (0x10000000 - PAGE_OFFSET) ? \
-		(PAGE_OFFSET + arm_dma_zone_size - 1) : 0xffffffffUL; })
+		min_t(phys_addr_t, (PAGE_OFFSET + arm_dma_zone_size - 1), 0xffffffffUL) : \
+		0xffffffffUL; })
 #endif
 
 #ifdef CONFIG_ISA_DMA_API
-- 
2.25.1