target/linux/generic/pending-4.9/332-arc-add-OWRTDTB-section.patch

   1 From: Alexey Brodkin <abrodkin@synopsys.com>
   2 Subject: openwrt: arc - add OWRTDTB section
   3
   4 This change allows OpenWRT to patch resulting kernel binary with
   5 external .dtb.
   6
   7 That allows us to re-use exactky the same vmlinux on different boards
   8 given its ARC core configurations match (at least cache line sizes etc).
   9
  10 ""patch-dtb" searches for ASCII "OWRTDTB:" strign and copies external
  11 .dtb right after it, keeping the string in place.
  12
  13 Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
  14 ---
  15  arch/arc/kernel/head.S        | 10 ++++++++++
  16  arch/arc/kernel/setup.c       |  4 +++-
  17  arch/arc/kernel/vmlinux.lds.S | 13 +++++++++++++
  18  3 files changed, 26 insertions(+), 1 deletion(-)
  19
  20 --- a/arch/arc/kernel/head.S
  21 +++ b/arch/arc/kernel/head.S
  22 @@ -59,6 +59,16 @@
  23  #endif
  24  .endm
  25
  26 +; Here "patch-dtb" will embed external .dtb
  27 +; Note "patch-dtb" searches for ASCII "OWRTDTB:" string
  28 +; and pastes .dtb right after it, hense the string precedes
  29 +; __image_dtb symbol.
  30 +       .section .owrt, "aw",@progbits
  31 +       .ascii  "OWRTDTB:"
  32 +ENTRY(__image_dtb)
  33 +       .fill   0x4000
  34 +END(__image_dtb)
  35 +
  36         .section .init.text, "ax",@progbits
  37
  38  ;----------------------------------------------------------------
  39 --- a/arch/arc/kernel/setup.c
  40 +++ b/arch/arc/kernel/setup.c
  41 @@ -444,7 +444,7 @@ ignore_uboot_args:
  42  #endif
  43
  44         if (use_embedded_dtb) {
  45 -               machine_desc = setup_machine_fdt(__dtb_start);
  46 +               machine_desc = setup_machine_fdt(&__image_dtb);
  47                 if (!machine_desc)
  48                         panic("Embedded DT invalid\n");
  49         }
  50 @@ -460,6 +460,8 @@ ignore_uboot_args:
  51         }
  52  }
  53
  54 +extern struct boot_param_header __image_dtb;
  55 +
  56  void __init setup_arch(char **cmdline_p)
  57  {
  58         handle_uboot_args();
  59 --- a/arch/arc/kernel/vmlinux.lds.S
  60 +++ b/arch/arc/kernel/vmlinux.lds.S
  61 @@ -30,6 +30,19 @@ SECTIONS
  62
  63         . = CONFIG_LINUX_LINK_BASE;
  64
  65 +       /*
  66 +        * In OpenWRT we want to patch built binary embedding .dtb of choice.
  67 +        * This is implemented with "patch-dtb" utility which searches for
  68 +        * "OWRTDTB:" string in first 16k of image and if it is found
  69 +        * copies .dtb right after mentioned string.
  70 +        *
  71 +        * Note: "OWRTDTB:" won't be overwritten with .dtb, .dtb will follow it.
  72 +        */
  73 +       .owrt : {
  74 +               *(.owrt)
  75 +               . = ALIGN(PAGE_SIZE);
  76 +       }
  77 +
  78         _int_vec_base_lds = .;
  79         .vector : {
  80                 *(.vector)