Documentation: Document a Broadwell refcode mod
Document how to modify the Broadwell refcode to support
the Intel GbE device.
Change-Id: I4f4f1e1c4ec2d79b3eb9f9c35fdc0330208e8509
Signed-off-by: Iru Cai <mytbk920423@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/75418
Reviewed-by: Felix Singer <service+coreboot-gerrit@felixsinger.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
diff --git a/Documentation/soc/intel/broadwell/blobs.md b/Documentation/soc/intel/broadwell/blobs.md
index b9f99af..01ce7c9 100644
--- a/Documentation/soc/intel/broadwell/blobs.md
+++ b/Documentation/soc/intel/broadwell/blobs.md
@@ -29,6 +29,25 @@
otherwise `refcode` will disable the Intel GbE device and the OS cannot find it
in the list of PCI devices.
+For the refcode binary extracted from Purism Librem 13 v1 (SHA256:
+8a919ffece61ba21664b1028b0ebbfabcd727d90c1ae2f72b48152b8774323a4,
+.program section starts at file offset 0x2040), we can see the
+following code sequence:
+
+ 1e06b: c6 43 0c 00 movb $0x0,0xc(%ebx)
+ 1e06f: c6 83 7e 03 00 00 00 movb $0x0,0x37e(%ebx)
+ 1e076: c6 83 70 03 00 00 01 movb $0x1,0x370(%ebx)
+ 1e07d: 66 89 43 0a mov %ax,0xa(%ebx)
+ 1e081: c6 83 da 01 00 00 01 movb $0x1,0x1da(%ebx)
+ 1e088: c6 83 86 03 00 00 01 movb $0x1,0x386(%ebx)
+
+The code at 0x1e06f sets the field that is to enable the GbE to the
+hardcoded 0 value. Change the byte at 0x1e075 (file offset 0x200b5)
+to 0x01 to make the refcode support Intel GbE:
+
+ cp refcode.elf refcode_gbe.elf
+ printf '\x01' | dd of=refcode_gbe.elf bs=1 seek=131253 count=1 conv=notrunc
+
## Use Broadwell SoC code for Haswell ULT boards
Haswell ULT boards can use Broadwell SoC code. To use Broadwell code for Haswell ULT