[meta-rockchip][PATCH v2] user-selectable wic compression

[Trevor Woerner <twoerner@gmail.com>]

For boards which build and boot wic images, the user can optionally specify
a compression using the WIC_COMPRESSION_EXTENSION variable. By default "wic"
images are built, but if the user would prefer, say "wic.xz" images, simply
specify:

	WIC_COMPRESSION_EXTENSION = ".xz"

in the configuration (e.g. conf/local.conf).

Signed-off-by: Trevor Woerner <twoerner@gmail.com>
---
v2 changes:
- change subject to specify "compression" not "format"
- add information in the README
- improve the commit message
- realize, thanks to Quentin's feedback, that this feature is used to help a
  user select a wic compression, not whether or not to use wic; as such, rename
  the variable and how it is used to emphasize this fact
---
 README                                | 11 +++++++++++
 conf/machine/include/rockchip-wic.inc |  5 ++++-
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/README b/README
index 605773d4ecd3..b21e92360dcc 100644
--- a/README
+++ b/README
@@ -47,6 +47,7 @@ Status of supported boards:
 
 Notes:
 -----
+  rk3308 rkbin:
 	The latest ddr initializer for the rk3308 platform does not output
 	diagnostic messages to uart0. This causes a bunch of gibberish to
 	be printed to the console window which only becomes legible once
@@ -67,6 +68,16 @@ Notes:
 	
 	in the configuration (e.g. conf/local.conf).
 
+  wic compression:
+	For boards which build and boot wic images, the user can optionally specify
+	a compression using the WIC_COMPRESSION_EXTENSION variable. By default "wic"
+	images are built, but if the user would prefer, say "wic.xz" images, simply
+	specify:
+
+		WIC_COMPRESSION_EXTENSION = ".xz"
+
+	in the configuration (e.g. conf/local.conf).
+
 U-Boot Environment:
 ------------------
 	In order to configure U-Boot to be able to store its environment into the
diff --git a/conf/machine/include/rockchip-wic.inc b/conf/machine/include/rockchip-wic.inc
index dab61d83ed2c..ebfc0cb96507 100644
--- a/conf/machine/include/rockchip-wic.inc
+++ b/conf/machine/include/rockchip-wic.inc
@@ -5,7 +5,10 @@ require conf/machine/include/rockchip-rk-u-boot-env.inc
 
 SPL_BINARY ?= "idbloader.img"
 
-IMAGE_FSTYPES += "wic wic.bmap"
+# if you use the following variable, make sure to add the '.' e.g.
+# WIC_COMPRESSION_EXTENSION = ".xz"
+WIC_COMPRESSION_EXTENSION ?= ""
+IMAGE_FSTYPES += "wic${WIC_COMPRESSION_EXTENSION} wic.bmap"
 WKS_FILE ?= "rockchip.wks"
 WKS_FILE_DEPENDS ?= " \
 	e2fsprogs-native \
-- 
2.44.0.478.g7774cfed6261