[yocto] questions about KBUILD_DEFCONFIG explanation in kernel-dev manual

[Robert P. J. Day]

  (yes, i really am digging through the user guides these days ...)

from kernel-dev manual, section 2.2.4:

  "To specify an "in-tree" defconfig file, edit the recipe that builds
   your kernel so that it has the following command form:

     KBUILD_DEFCONFIG_KMACHINE ?= defconfig_file

   You need to append the variable with KMACHINE and then supply the
   path to your "in-tree" defconfig file."

first, i'm going to tag the "KMACHINE" part above with
<replaceable>, since it pretty clearly needs it.

  next, you need to "supply the path" to the defconfig file? uh, don't
you just need to give the simple name of the in-tree defconfig file
you want to use as it is somewhere under arch/<arch>/configs in the
kernel source tree? here's a snippet from the meta-altera layer:

   KBUILD_DEFCONFIG ?= "socfpga_defconfig"
   KBUILD_DEFCONFIG_stratix10swvp ?= "defconfig"
   KBUILD_DEFCONFIG_10m50 ?= "10m50_defconfig"

seems like one needs just the name of the defconfig file to be used,
there's no concept of needing a "path" to the file, is there?

  next, it appears that one does *not* "need to append the variable
with KMACHINE", given one of the lines from meta-altera above, is that
correct? this just sets a default, no?

   KBUILD_DEFCONFIG ?= "socfpga_defconfig"

  and finally, must all defconfig files identified via
KBUILD_DEFCONFIG be an "in-tree" file? i ask since this line above:

   KBUILD_DEFCONFIG_stratix10swvp ?= "defconfig"

is potentially confusing, and might make someone perusing the source
to think that's an alternative way to point at their "out-of-tree"
defconfig file. but it's not, is it?

  i checked that machine type, and it's armv8, so i'm *assuming* that
line would refer to the in-tree file arch/arm64/configs/defconfig, is
that right?

  i think that will do it for now.

rday

-- 

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Robert P. J. Day                                 Ottawa, Ontario, CANADA
                        http://crashcourse.ca

Twitter:                                       http://twitter.com/rpjday
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