Enabling runtime P2V by default (Re: [PATCH 3/5] mach-u300: patch physoffset by default)

[Russell King - ARM Linux]

On Wed, Aug 10, 2011 at 10:29:55AM +0100, Russell King - ARM Linux wrote:
> On Wed, Aug 10, 2011 at 10:22:06AM +0100, Will Deacon wrote:
> > On Wed, Aug 10, 2011 at 10:16:35AM +0100, Russell King - ARM Linux wrote:
> > > On Tue, Aug 09, 2011 at 09:41:38PM +0200, Linus Walleij wrote:
> > > > From: Linus Walleij <linus.walleij at linaro.org>
> > > > 
> > > > This works like a charm so I'll just default-select it.
> > > 
> > > Well, we can remove the EXPERIMENTAL status of this option now.  This
> > > raises the question is whether we should now default it to 'y' - I
> > > think we should.  Anyone have any objections?
> > 
> > I've been running with this option enabled for the collection of ARM boards
> > I have and the only problem I have encountered was related to u-boot loading
> > at the wrong address.
> > 
> > So I'm all for enabling it by default, especially since it will force out
> > any remaining issues for boards where this hasn't been used extensively.
> 
> Maybe also making the option hidden depending on EXPERT, or even EMBEDDED
> would be a good idea too.  I think it falls into at least the same class
> as UID16, sysctl, hotplug, printk, etc. which are all EXPERT options.

Right, I'm now committing a patch to hide the option unless EMBEDDED
is enabled.  I think this means we should get rid of the 'select
ARM_PATCH_PHYS_VIRT' statements from the various platforms, so that
folk can optimize away that code if they know what they're doing.

Note: this patch will conflict with the removal of the 16-bit P2V
patching, so we need to sort that out.

8<---------
From: Russell King - ARM Linux <linux at arm.linux.org.uk>
ARM: enable ARM_PATCH_PHYS_VIRT by default

Enable virtual to physical translation patching by default in all
kernels.  Hide the option behind EMBEDDED.

This can still be turned off if people desire, and they know what
they're doing, to shrink the size of the kernel to a minimum.

Signed-off-by: Russell King <rmk+kernel at arm.linux.org.uk>
---
 arch/arm/Kconfig |    8 ++++++--
 1 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 5ebc5d9..6085a6c 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -195,7 +195,8 @@ config VECTORS_BASE
 	  The base address of exception vectors.
 
 config ARM_PATCH_PHYS_VIRT
-	bool "Patch physical to virtual translations at runtime"
+	bool "Patch physical to virtual translations at runtime" if EMBEDDED
+	default y
 	depends on !XIP_KERNEL && MMU
 	depends on !ARCH_REALVIEW || !SPARSEMEM
 	help
@@ -207,6 +208,10 @@ config ARM_PATCH_PHYS_VIRT
 	  of physical memory is at a 16MB boundary, or theoretically 64K
 	  for the MSM machine class.
 
+	  Only disable this option if you know what you do not require
+	  this feature (eg, building a kernel for a single machine) and
+	  you need to shrink the kernel to the minimal size.
+
 config ARM_PATCH_PHYS_VIRT_16BIT
 	def_bool y
 	depends on ARM_PATCH_PHYS_VIRT && ARCH_MSM
@@ -301,7 +306,6 @@ config ARCH_AT91
 	select ARCH_REQUIRE_GPIOLIB
 	select HAVE_CLK
 	select CLKDEV_LOOKUP
-	select ARM_PATCH_PHYS_VIRT if MMU
 	help
 	  This enables support for systems based on the Atmel AT91RM9200,
 	  AT91SAM9 and AT91CAP9 processors.
-- 
1.7.4.4