It's quite common to have an external watchdog which is serviced via
flipping a GPIO, with the value of that GPIO being settable directly
in a memory-mapped register. So add kconfig options defining the
physical address of such a register as well as a mask to have the
decompressor periodically xor into that register.
If and when other decompress_keepalive methods are added, this can be
made into a "choice DECOMPRESS_KEEPALIVE".
Since only LZ4 is wired up currently, this is "depends on KERNEL_LZ4"
for now. Also, prevent this option from being shown to the average
user.
Signed-off-by: Rasmus Villemoes <li...@rasmusvillemoes.dk>
---
include/linux/decompress/keepalive.h | 8 +++++++
init/Kconfig | 33 ++++++++++++++++++++++++++++
2 files changed, 41 insertions(+)
diff --git a/include/linux/decompress/keepalive.h
b/include/linux/decompress/keepalive.h
index 39caa7693624..c62e49bee7cf 100644
--- a/include/linux/decompress/keepalive.h
+++ b/include/linux/decompress/keepalive.h
@@ -5,6 +5,14 @@
#ifdef PREBOOT
+#ifdef CONFIG_DECOMPRESS_KEEPALIVE_TOGGLE
+#define decompress_keepalive() do { \
+ long addr = CONFIG_DECOMPRESS_KEEPALIVE_TOGGLE_REG; \
+ volatile unsigned *reg = (volatile unsigned *)addr; \
+ *reg ^= CONFIG_DECOMPRESS_KEEPALIVE_TOGGLE_MASK; \
+} while (0)
+#endif
+
#endif
#ifndef decompress_keepalive
diff --git a/init/Kconfig b/init/Kconfig
index b4daad2bac23..8a894d9fdd77 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -289,6 +289,39 @@ config KERNEL_UNCOMPRESSED
endchoice
+config DECOMPRESS_KEEPALIVE_TOGGLE
+ depends on KERNEL_LZ4
+ depends on EXPERT
+ bool "Toggle some bits while decompressing"
+ help
+ Some embedded boards have an always-running hardware
+ watchdog with a timeout short enough that the board is reset
+ during decompression, thus preventing the board from ever
+ booting.
+
+ Enable this to toggle certain bits in a memory register
+ while decompressing the kernel. This can for example be used
+ in the common case of an external watchdog serviced via a
+ memory-mapped GPIO.
+
+ Say N unless you know you need this.
+
+if DECOMPRESS_KEEPALIVE_TOGGLE
+
+config DECOMPRESS_KEEPALIVE_TOGGLE_REG
+ hex "Address of register to modify while decompressing"
+ help
+ Set this to a physical address of a 32-bit memory word to
+ modify while decompressing.
+
+config DECOMPRESS_KEEPALIVE_TOGGLE_MASK
+ hex "Bit mask to toggle while decompressing"
+ help
+ The register selected above will periodically be xor'ed with
+ this value during decompression.
+
+endif
+
config DEFAULT_HOSTNAME
string "Default hostname"
default "(none)"
--
2.20.1
