[PATCH] arch: arm: mach-imx: document field return in CSF template

[Bastian Krause]

Activating the field return configuration returns a locked-down board
(nearly) to its open state. In order to burn the FIELD_RETURN fuse, the
CSF must contain a specific unlock command with the device's UID.

Signed-off-by: Bastian Krause <bst at pengutronix.de>
---
 .../include/mach/habv4-imx6-gencsf-template.h        | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/arch/arm/mach-imx/include/mach/habv4-imx6-gencsf-template.h b/arch/arm/mach-imx/include/mach/habv4-imx6-gencsf-template.h
index a60b485292..45da2981cb 100644
--- a/arch/arm/mach-imx/include/mach/habv4-imx6-gencsf-template.h
+++ b/arch/arm/mach-imx/include/mach/habv4-imx6-gencsf-template.h
@@ -39,6 +39,18 @@ hab Engine = SETUP_HABV4_ENGINE
 hab Features = SETUP_HABV4_FEATURES
 #endif
 
+/*
+// allow fusing FIELD_RETURN
+// # ocotp0.permanent_write_enable=1
+// # mw -l -d /dev/imx-ocotp 0xb8 0x1
+hab [Unlock]
+hab Engine = OCOTP
+hab Features = FIELD RETURN
+// device-specific UID:
+// $ dd if=/sys/bus/nvmem/devices/imx-ocotp0/nvmem bs=4 skip=1 count=2 status=none | hexdump -ve '1/1 "0x%.2x, "' | sed 's/, $//'
+hab UID = 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08
+*/
+
 hab [Install Key]
 /* verification key index in key store (0, 2...4) */
 hab Verification index = 0
-- 
2.30.2