Messages in this thread | | | Date | Tue, 24 Nov 2015 20:35:16 +0000 | From | Russell King - ARM Linux <> | Subject | Re: [RFC/PATCH 0/3] ARM: Use udiv/sdiv for __aeabi_{u}idiv library functions |
| |
On Tue, Nov 24, 2015 at 12:07:30PM -0800, Stephen Boyd wrote: > Ok. Presumably the order of arch-$(CONFIG) lines in the Makefile > are done in an order to allow the build to degrade to the lowest > common denominator among architecture support.
Correct. Make processes the directives in the order listed in the makefile, which means that a variable final value results from its last assignment.
> CPU_V7 selects > CPU_32v7 and we're using that config to select -march=armv7-a in > the Makefile. The patch currently uses CPU_32v7VE to select > -march=armv7ve. If CPU_V7VE selects CPU_V7 we'll never be able to > use -march=armv7ve because CPU_V7 will be selecting CPU_32v7 and > that will come after CPU_32v7VE in the Makefile.
Right, but look at how the V6K stuff is handled:
arch-$(CONFIG_CPU_32v6) =-D__LINUX_ARM_ARCH__=6 $(call cc-option,-march=armv6,-march=armv5t -Wa$(comma)-march=armv6) # Only override the compiler option if ARMv6. The ARMv6K extensions are # always available in ARMv7 ifeq ($(CONFIG_CPU_32v6),y) arch-$(CONFIG_CPU_32v6K) =-D__LINUX_ARM_ARCH__=6 $(call cc-option,-march=armv6k,-march=armv5t -Wa$(comma)-march=armv6k) endif
We'd need to do something similar for v7VE as well. As we're getting more of this, I'd suggest we move to:
arch-v7a-y =$(call cc-option,-march=armv7-a,-march=armv5t -Wa$(comma)-march=armv7-a) arch-v7a-$(CONFIG_CPU_32v7VE) =... whatever it was... arch-$(CONFIG_CPU_32v7) =-D__LINUX_ARM_ARCH__=7 $(arch-v7a-y) arch-v6-y =$(call cc-option,-march=armv6,-march=armv5t -Wa$(comma)-march=armv6) arch-v6-$(CONFIG_CPU_32v6K) =$(call cc-option,-march=armv6k,-march=armv5t -Wa$(comma)-march=armv6k) arch-$(CONFIG_CPU_32v6) =-D__LINUX_ARM_ARCH__=6 $(arch-v6-y)
> My understanding is that we want to support CPU_V7VE without > CPU_V7 enabled so that it uses the idiv instructions in that > configuration. When V7VE and V7 are both enabled, we should > degrade to the aeabi functions, and the same is true for when > V7VE is disabled.
Let me have another look at this, it's been a while since I touched these options...
-- FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up according to speedtest.net.
| |