powerpc/boot: Fix build failures with -j 1

[Michael Ellerman]

On Thu, 2018-12-06 at 05:10:28 UTC, Michael Ellerman wrote:
> In commit 5e9dcb6188a4 ("powerpc/boot: Expose Kconfig symbols to
> wrapper") we added a dependency to serial.c on autoconf.h:
> 
>   $(obj)/serial.c: $(obj)/autoconf.h
> 
> This works when building in-tree (ie. with KBUILD_OUTPUT unset)
> because the obj tree is the src tree.
> 
> But when building with eg. O=build and -j 1 the build fails:
> 
>   gcc ... -I../arch/powerpc/boot -c -o arch/powerpc/boot/serial.o arch/powerpc/boot/serial.c
>   gcc: error: arch/powerpc/boot/serial.c: No such file or directory
> 
> Why this is only happening with -j 1 is not clear, when building with
> -j greater than 1 somehow we decide to look for serial.c in the src
> tree (../), eg:
> 
>   gcc -I../arch/powerpc/boot -c -o arch/powerpc/boot/serial.o ../arch/powerpc/boot/serial.c
> 
> Regardless we shouldn't be specifying a dependency on serial.c in the
> build tree, we want to add a dependency to the version in $(srctree)
> so fix the rule to say that.
> 
> Fixes: 5e9dcb6188a4 ("powerpc/boot: Expose Kconfig symbols to wrapper")
> Tested-by: Daniel Axtens <dja at axtens.net>
> Signed-off-by: Michael Ellerman <mpe at ellerman.id.au>

Applied to powerpc fixes.

https://git.kernel.org/powerpc/c/e41b93a6be57e26a4a123345f826a6

cheers