of: select OF_RESERVED_MEM automatically

The OF_RESERVED_MEM can be used if we have either CMA or the generic
declare coherent code built and we support the early flattened DT.

So don't bother making it a user visible options that is selected
by most configs that fit the above category, but just select it when
the requirements are met.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Rob Herring <robh@kernel.org>

arch/arc/Kconfig

@@ -45,7 +45,6 @@ config ARC
 	select MODULES_USE_ELF_RELA
 	select OF
 	select OF_EARLY_FLATTREE
-	select OF_RESERVED_MEM
 	select PCI_SYSCALL if PCI
 	select PERF_USE_VMALLOC if ARC_CACHE_VIPT_ALIASING
 

arch/arm/Kconfig

@@ -103,7 +103,6 @@ config ARM
 	select MODULES_USE_ELF_REL
 	select NEED_DMA_MAP_STATE
 	select OF_EARLY_FLATTREE if OF
-	select OF_RESERVED_MEM if OF
 	select OLD_SIGACTION
 	select OLD_SIGSUSPEND3
 	select PCI_SYSCALL if PCI

arch/arm64/Kconfig

@@ -165,7 +165,6 @@ config ARM64
 	select NEED_SG_DMA_LENGTH
 	select OF
 	select OF_EARLY_FLATTREE
-	select OF_RESERVED_MEM
 	select PCI_DOMAINS_GENERIC if PCI
 	select PCI_ECAM if (ACPI && PCI)
 	select PCI_SYSCALL if PCI

arch/csky/Kconfig

@@ -42,7 +42,6 @@ config CSKY
 	select MODULES_USE_ELF_RELA if MODULES
 	select OF
 	select OF_EARLY_FLATTREE
-	select OF_RESERVED_MEM
 	select PERF_USE_VMALLOC if CPU_CK610
 	select RTC_LIB
 	select TIMER_OF

arch/powerpc/Kconfig

@@ -233,7 +233,6 @@ config PPC
 	select NEED_SG_DMA_LENGTH
 	select OF
 	select OF_EARLY_FLATTREE
-	select OF_RESERVED_MEM
 	select OLD_SIGACTION			if PPC32
 	select OLD_SIGSUSPEND
 	select PCI_DOMAINS			if PCI

arch/xtensa/Kconfig

@@ -447,7 +447,6 @@ config USE_OF
 	bool "Flattened Device Tree support"
 	select OF
 	select OF_EARLY_FLATTREE
-	select OF_RESERVED_MEM
 	help
 	  Include support for flattened device tree machine descriptions.
 

drivers/of/Kconfig

@@ -81,10 +81,9 @@ config OF_MDIO
 	  OpenFirmware MDIO bus (Ethernet PHY) accessors
 
 config OF_RESERVED_MEM
-	depends on OF_EARLY_FLATTREE
 	bool
-	help
-	  Helpers to allow for reservation of memory regions
+	depends on OF_EARLY_FLATTREE
+	default y if HAVE_GENERIC_DMA_COHERENT || DMA_CMA
 
 config OF_RESOLVE
 	bool