linux-kernel - Re: [PATCH 02/60] microblaze_v4: Makefiles for Microblaze cpu

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Message-ID: <20080626194002.GC22827@cs181140183.pp.htv.fi>
Date:	Thu, 26 Jun 2008 22:40:02 +0300
From:	Adrian Bunk <bunk@...nel.org>
To:	Michal Simek <monstr@...nam.cz>
Cc:	linux-kernel@...r.kernel.org, arnd@...db.de,
	linux-arch@...r.kernel.org, stephen.neuendorffer@...inx.com,
	John.Linn@...inx.com, john.williams@...alogix.com, matthew@....cx,
	will.newton@...il.com, drepper@...hat.com,
	microblaze-uclinux@...e.uq.edu.au, grant.likely@...retlab.ca,
	linuxppc-dev@...abs.org, vapier.adi@...il.com,
	alan@...rguk.ukuu.org.uk, hpa@...or.com
Subject: Re: [PATCH 02/60] microblaze_v4: Makefiles for Microblaze cpu

On Thu, Jun 26, 2008 at 08:46:44PM +0200, Michal Simek wrote:
> Adrian Bunk napsal(a):
> > On Thu, Jun 26, 2008 at 02:29:31PM +0200, monstr@...nam.cz wrote:
> >> ...
> >> --- /dev/null
> >> +++ b/arch/microblaze/Makefile
> >> ...
> >> +# Work out HW multipler support.  This is icky.
> >> +# 1. Spartan2 has no HW multiplers.
> >> +# 2. MicroBlaze v3.x always uses them, except in Spartan 2
> >> +# 3. All other FPGa/CPU ver combos, we can trust the CONFIG_ settings
> >> +ifeq (,$(findstring spartan2,$(CONFIG_XILINX_MICROBLAZE0_FAMILY)))
> >> +  ifeq ($(CPU_MAJOR),3)
> >> +    CPUFLAGS-1 += -mno-xl-soft-mul
> >> +  else
> >> +    # USE_HW_MUL can be 0, 1, or 2, defining a heirarchy of HW Mul support.
> >> +    CPUFLAGS-$(subst 1,,$(CONFIG_XILINX_MICROBLAZE0_USE_HW_MUL)) += -mxl-multiply-high
> >> +    CPUFLAGS-$(CONFIG_XILINX_MICROBLAZE0_USE_HW_MUL) += -mno-xl-soft-mul
> >> +  endif
> >> +endif
> >> +CPUFLAGS-$(CONFIG_XILINX_MICROBLAZE0_USE_DIV) += -mno-xl-soft-div
> >> +CPUFLAGS-$(CONFIG_XILINX_MICROBLAZE0_USE_BARREL) += -mxl-barrel-shift
> >> +CPUFLAGS-$(CONFIG_XILINX_MICROBLAZE0_USE_PCMP) += -mxl-pattern-compare
> >> +
> >> +CPUFLAGS-1 += $(call cc-option,-mcpu=v$(CPU_VER))
> >> +
> >> +# The various CONFIG_XILINX cpu features options are integers 0/1/2...
> >> +# rather than bools y/n
> >> +CFLAGS += $(CPUFLAGS-1)
> >> +CFLAGS += $(CPUFLAGS-2)
> >> ...
> > 
> > Why are the options not bools?
> > 
> > cu
> > Adrian
> 
> because CONFIG_XILINX_... are 0, 1 or 2 not only y, n.

I understood that.

But _why_ are these options not bools?

In most cases the order of gcc flags does not matter, and it is not 
obvious for me why the order matters here.

> M

cu
Adrian

-- 

       "Is there not promise of rain?" Ling Tan asked suddenly out
        of the darkness. There had been need of rain for many days.
       "Only a promise," Lao Er said.
                                       Pearl S. Buck - Dragon Seed

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