[PATCH] x86, 64: let zone DMA cover low 4G if no ISA-style devices

[Baoquan He]

It doesn't make sense to let the rare legacy ISA-style devies
drag x86_64 to have a tiny zone DMA of 16M which cause many
troubles.

Signed-off-by: Baoquan He <bhe@xxxxxxxxxx>
---
 arch/x86/Kconfig   | 1 -
 arch/x86/mm/init.c | 5 ++++-
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 5aa4c2ecf5c7..93af781f9445 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2761,7 +2761,6 @@ config ISA_BUS
 # x86_64 have no ISA slots, but can have ISA-style DMA.
 config ISA_DMA_API
 	bool "ISA-style DMA support" if (X86_64 && EXPERT)
-	default y
 	help
 	  Enables ISA-style DMA support for devices requiring such controllers.
 	  If unsure, say Y.
diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
index 82a042c03824..c9ffb38dcc6a 100644
--- a/arch/x86/mm/init.c
+++ b/arch/x86/mm/init.c
@@ -1024,9 +1024,12 @@ void __init zone_sizes_init(void)
 
 	memset(max_zone_pfns, 0, sizeof(max_zone_pfns));
 
-#ifdef CONFIG_ZONE_DMA
+#if defined(CONFIG_ZONE_DMA) && defined(CONFIG_ISA_DMA_API)
 	max_zone_pfns[ZONE_DMA]		= min(MAX_DMA_PFN, max_low_pfn);
+#else
+	max_zone_pfns[ZONE_DMA]		= min(MAX_DMA32_PFN, max_low_pfn);
 #endif
+
 #ifdef CONFIG_ZONE_DMA32
 	max_zone_pfns[ZONE_DMA32]	= min(MAX_DMA32_PFN, max_low_pfn);
 #endif
-- 
2.34.1