[RFC v2 PATCH 23/23] ARM: Allow ARCH_MULTIPLATFORM to be selected for NOMMU

[Vladimir Murzin]

On 29/11/16 17:22, Russell King - ARM Linux wrote:
> On Tue, Nov 29, 2016 at 12:40:05PM +0000, Vladimir Murzin wrote:
>> With this patch applied potentially any platform can be built in NOMMU
>> configurations if CONFIG_EXPERT is selected. However, there is no
>> guaranty that platform can successfully run such Image. So the main
> 
> guarantee
> 
>> 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 at visionengravers.com>
>> Cc: Ryan Mallon <rmallon at gmail.com>
>> Cc: Tony Lindgren <tony at atomide.com>
>> Cc: Thierry Reding <thierry.reding at gmail.com>
>> Cc: Alexander Shiyan <shc_work at mail.ru>
>> Cc: Shawn Guo <shawnguo at kernel.org>
>> Cc: Sascha Hauer <kernel at pengutronix.de>
>> Cc: Fabio Estevam <fabio.estevam at nxp.com>
>> Cc: Linus Walleij <linus.walleij at linaro.org>
>> Cc: Russell King <linux at armlinux.org.uk>
>> Signed-off-by: Vladimir Murzin <vladimir.murzin at arm.com>
>> ---
>>  arch/arm/Kconfig |   21 +++++++++++++++++++--
>>  1 file changed, 19 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
>> index e78c822..bc6f406 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.
> 
> Do you actually see this help text anywhere?  I don't think multiple-choice
> options show help for individual choices.
> 

Yes I can: "System Type" -> "ARM system type" -> "Allow multiple platforms to
be selected" -> "?". Probably not the best place, but I failed to find
anything better :(

Cheers
Vladimir