[U-Boot] armv5 and OMAP3 Question

[Tom Rini <trini@konsulko.com>]

On Fri, Aug 03, 2018 at 10:02:17AM -0500, Adam Ford wrote:
> On Fri, Aug 3, 2018 at 10:00 AM Tom Rini <trini@konsulko.com> wrote:
> >
> > On Fri, Aug 03, 2018 at 05:43:46AM -0500, Adam Ford wrote:
> > > On Tue, Jul 25, 2017 at 11:08 AM Tom Rini <trini@konsulko.com> wrote:
> > > >
> > > > On Tue, Jul 25, 2017 at 08:14:57AM -0500, Adam Ford wrote:
> > > >
> > > > > The readme file for OMAP indicates that we compile using armv5 to "to
> > > > > allow more compilers to work"
> > > > >
> > > > > We have our arch/arm/mach-omap2/omap3/lowlevel_init.S file also noting
> > > > > some special assembly insturctions becuse we use armv5.  The barriers
> > > > > defined also indicate we're using CP15 instead of the separate barrier
> > > > > instructions for armv7 because we're using armv5 instead.
> > > > >
> > > > > I just wonder in this day and age when we're noting a GCC version and
> > > > > generating warnings based on the GCC warning, do we still need to
> > > > > compile as armv5 any more?  It seems like "to allow more compilers to
> > > > > work" would not really apply any more we're trying to push newer
> > > > > versions of GCC.
> > > >
> > > > So, these are historical notes that really should be corrected.
> > > > Initially, when ARMv7 support was added, most people did not have
> > > > compilers new enough to recognize -march=armv7-a.  We still even support
> > > > them, see the logic in arch/arm/Makefile around CONFIG_CPU_V7 (the
> > > > options are any sort of modern gcc, llvm, ancient gcc).  When we move to
> > > > gcc-6 being the oldest gcc supported for ARM we can fixup those comments
> > > > and logic as well.
> > >
> > > My understanding is that we've made the requirement for GCC 6 now.  I
> > > just pushed a patch which enabled mtune=armv7-a-generic when
> > > CONFIG_CPU_V7A is enabled and that seems to shrink the code a bit on
> > > omap3_logic.  Does it make sense to remove the , -march=armv5 from
> > > arch/arm/Makefile and or the plain -march=armv7 since CONFIG_CPU_V7A
> > > implies armv-a?
> >
> > Yes, we can probably at least drop the v5 portion of that logic.  As
> > noted in the other patch, LLVM and GCC disagree on "armv7" vs "armv7-a"
> > as being the appropriate name, or at least did in the past.
> 
> Can you point me to an example of how to tune armv7 for both GCC and
> LLVM?  I was looking around and I'm not seeing an obvious syntax.
> I'll do a 2-part patch.  One to remove the armv5, and one to enable
> the armv7 optimization.

In arch/arm/Makefile:
arch-$(CONFIG_CPU_V7A)          =$(call cc-option, -march=armv7-a, \
                                 $(call cc-option, -march=armv7, -march=armv5))

this works in both cases.  And doc/README.clang is correct on how to
build with LLVM on ARM.

-- 
Tom
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