[RFC v3 PATCH 25/25] ARM: Allow ARCH_MULTIPLATFORM to be selected for NOMMU

Vladimir Murzin
2016-12-02T15:05:43Z

With this patch applied potentially any platform can be built in NOMMU
configurations if CONFIG_EXPERT is selected. However, there is no
guarantee that platform can successfully run such Image. So the main
motivation behind of this patch:
- bring build coverage for NOMMU configurations
- allow known working NOMMU platforms (like R-class) to be used
- pave a way to add support for single address space (aka 1:1 mapping)
for MMU platforms, so they can be usable in NOMMU configurations

Cc: Hartley Sweeten <hsweeten@visionengravers.com>
Cc: Ryan Mallon <rmallon@gmail.com>
Cc: Tony Lindgren <tony@atomide.com>
Cc: Thierry Reding <thierry.reding@gmail.com>
Cc: Alexander Shiyan <shc_work@mail.ru>
Cc: Shawn Guo <shawnguo@kernel.org>
Cc: Sascha Hauer <kernel@pengutronix.de>
Cc: Fabio Estevam <fabio.estevam@nxp.com>
Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: Russell King <linux@armlinux.org.uk>
Signed-off-by: Vladimir Murzin <vladimir.murzin@arm.com>
---
arch/arm/Kconfig | 21 +++++++++++++++++++--
1 file changed, 19 insertions(+), 2 deletions(-)

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index b3fa6e9..9c90b81 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -327,9 +327,9 @@ choice

config ARCH_MULTIPLATFORM
bool "Allow multiple platforms to be selected"
- depends on MMU
+ depends on MMU || EXPERT
select ARM_HAS_SG_CHAIN
- select ARM_PATCH_PHYS_VIRT
+ select ARM_PATCH_PHYS_VIRT if MMU
select AUTO_ZRELADDR
select CLKSRC_OF
select COMMON_CLK
@@ -339,6 +339,23 @@ config ARCH_MULTIPLATFORM
select PCI_DOMAINS if PCI
select SPARSE_IRQ
select USE_OF
+ help
+ Please, read carefully if you've selected CONFIG_MMU=n!
+
+ Multiplatform with !MMU configuration *is not* meant that
+ kernel built to support every platform will boot on them. It
+ is because physical address space layouts (particularly where
+ RAM is located) are different between platforms and there is
+ no MMU to work that around.
+
+ You must specify where RAM start (via DRAM_BASE config
+ option) and appropriate size of RAM (via DRAM_SIZE config
+ option) which are valid for the platform you are building
+ for.
+
+ This feature is *EXPERIMENTAL*, please, consider building
+ with CONFIG_MMU=y unless you know what you do or want to
+ help with testing.

config ARM_SINGLE_ARMV7M
bool "ARMv7-M based platforms (Cortex-M0/M3/M4)"
--
1.7.9.5