MIPS: generic: Select MIPS_AUTO_PFN_OFFSET

This change “MIPS: generic: Select MIPS_AUTO_PFN_OFFSET” in Linux kernel is authored by Paul Burton <paul.burton [at] mips.com> on Fri Jul 27 18:23:21 2018 -0700.

MIPS: generic: Select MIPS_AUTO_PFN_OFFSET

Enable CONFIG_MIPS_AUTO_PFN_OFFSET for the generic platform, allowing
it to avoid wasted book-keeping for pages with addresses lower than the
physical base address of memory.

This has a minimal impact on kernel text size, with 64r6el_defconfig
gaining 0.1% in size as reported by bloat-o-meter:

  add/remove: 4/1 grow/shrink: 345/13 up/down: 9017/-392 (8625)
  Function                                     old     new   delta
  pcpu_setup_first_chunk                      1444    1780    +336
  pcpu_alloc_first_chunk                       864    1136    +272
  start_kernel                                1064    1288    +224
  initcall_blacklist                           224     372    +148
  try_fill_recv                               2088    2184     +96
  ...
  Total: Before=8457273, After=8465898, chg +0.10%

The gain for systems with large offsets to physical memory & the ability
to continue using generic kernels on such systems seems well worth this
small cost.

Signed-off-by: Paul Burton <paul.burton@mips.com>
Suggested-by: Vladimir Kondratiev <vladimir.kondratiev@intel.com>
Patchwork: https://patchwork.linux-mips.org/patch/20049/
Cc: James Hogan <jhogan@kernel.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org

This Linux change may have been applied to various maintained Linux releases and you can find Linux releases including commit 0211d49.

There is one line of Linux source code added/deleted in this change. Code changes to Linux kernel are as follows.

 arch/mips/Kconfig | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
index fbf7f67..c95eb5a 100644
--- a/arch/mips/Kconfig
+++ b/arch/mips/Kconfig
@@ -98,6 +98,7 @@ config MIPS_GENERIC
 	select HW_HAS_PCI
 	select IRQ_MIPS_CPU
 	select LIBFDT
+	select MIPS_AUTO_PFN_OFFSET
 	select MIPS_CPU_SCACHE
 	select MIPS_GIC
 	select MIPS_L1_CACHE_SHIFT_7

The commit for this change in Linux stable tree is 0211d49 (patch).

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