Re: Question about ARM FASTFPE

[Russell King - ARM Linux admin]

On Wed, Jul 10, 2019 at 06:54:06PM +0900, Masahiro Yamada wrote:
> On Wed, Jul 10, 2019 at 5:23 PM Russell King - ARM Linux admin
> <linux@xxxxxxxxxxxxxxx> wrote:
> >
> > On Wed, Jul 10, 2019 at 01:30:24PM +0900, Masahiro Yamada wrote:
> > > Hi.
> > >
> > > I have a question about the following code
> > > in arch/arm/Makefile:
> > >
> > >
> > > # Do we have FASTFPE?
> > > FASTFPE :=arch/arm/fastfpe
> > > ifeq ($(FASTFPE),$(wildcard $(FASTFPE)))
> > > FASTFPE_OBJ :=$(FASTFPE)/
> > > endif
> > >
> > >
> > > Since arch/arm/fastfpe does not exist in the upstream tree,
> > > I guess this is a hook to compile downstream source code.
> > >
> > > If a user puts arch/arm/fastfpe/ into their local source tree,
> > > Kbuild is supposed to compile the files in it.
> > >
> > > Is this correct?
> > >
> > >
> > > If so, I am afraid this would not work for O= building.
> > >
> > > $(wildcard ...) checks if this directory exists in the *objtree*,
> > > while scripts/Makefile.build needs to include
> > > arch/arm/fastfpe/Makefile from *srctree*.
> > >
> > > I think the correct code should be like follows:
> > >
> > > # Do we have FASTFPE?
> > > FASTFPE :=arch/arm/fastfpe
> > > ifneq ($(wildcard $(srctree)/$(FASTFPE)),)
> > > FASTFPE_OBJ :=$(FASTFPE)/
> > > endif
> > >
> > >
> > > Having said that, I am not sure this code is worth fixing.
> > >
> > > This code was added around v2.5.1.9,
> >
> > ... as a _result_ of a discussion and deciding not to upstream it,
> > but to still allow its use.  Fastfpe is faster than nwfpe (so has
> > a definite advantage for FP intensive applications) but we decided
> > we didn't want two FP emulation codes in the kernel.  However, if
> > someone wants to use it, it has to be built into the kernel, it
> > can't be modular.
> 
> 
> IMHO, the entry in Makefile and Kconfig should be removed
> from upstream, then moved to a part of the fastfpe local patch.

Nope.  It means that rather than it being merely a drop-in, it has
to be maintained against changes to both these files.  Sorry, that's
more work.

-- 
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