[tip:x86/microcode] x86/microcode: Document builtin microcode loading method

[tip-bot for Borislav Petkov]

Commit-ID:  b584303261b7041f209afde4bf7ddb7a21598a1f
Gitweb:     http://git.kernel.org/tip/b584303261b7041f209afde4bf7ddb7a21598a1f
Author:     Borislav Petkov <bp@xxxxxxx>
AuthorDate: Wed, 3 Feb 2016 12:33:45 +0100
Committer:  Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Tue, 9 Feb 2016 11:41:19 +0100

x86/microcode: Document builtin microcode loading method

Add some text and an example to Documentation/x86/early-microcode.txt
explaining how to build in microcode.

Tested-by: Thomas Voegtle <tv@xxxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/1454499225-21544-18-git-send-email-bp@xxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 Documentation/x86/early-microcode.txt | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/Documentation/x86/early-microcode.txt b/Documentation/x86/early-microcode.txt
index d62bea6..c956d99 100644
--- a/Documentation/x86/early-microcode.txt
+++ b/Documentation/x86/early-microcode.txt
@@ -40,3 +40,28 @@ cp ../microcode.bin kernel/x86/microcode/GenuineIntel.bin (or AuthenticAMD.bin)
 find . | cpio -o -H newc >../ucode.cpio
 cd ..
 cat ucode.cpio /boot/initrd-3.5.0.img >/boot/initrd-3.5.0.ucode.img
+
+Builtin microcode
+=================
+
+We can also load builtin microcode supplied through the regular firmware
+builtin method CONFIG_FIRMWARE_IN_KERNEL. Here's an example:
+
+CONFIG_FIRMWARE_IN_KERNEL=y
+CONFIG_EXTRA_FIRMWARE="intel-ucode/06-3a-09 amd-ucode/microcode_amd_fam15h.bin"
+CONFIG_EXTRA_FIRMWARE_DIR="/lib/firmware"
+
+This basically means, you have the following tree structure locally:
+
+/lib/firmware/
+|-- amd-ucode
+...
+|   |-- microcode_amd_fam15h.bin
+...
+|-- intel-ucode
+...
+|   |-- 06-3a-09
+...
+
+so that the build system can find those files and integrate them into
+the final kernel image. The early loader finds them and applies them.