[PATCH v4 4/5] env: Allow environment files to use the C preprocessor

[Simon Glass <sjg@chromium.org>]

In many cases environment variables need access to the U-Boot CONFIG
variables to select different options. Enable this so that the environment
scripts can be as useful as the ones currently in the board config files.

Also support += to allow variables to be appended to. This is needed when
using the preprocessor.

Signed-off-by: Simon Glass <sjg@chromium.org>
---

Changes in v4:
- Add documentation in rST format instead of README

Changes in v3:
- Define __UBOOT_CONFIG__ when collecting environment files

Changes in v2:
- Add separate patch to enable C preprocessor for environment files
- Enable var+=value form to simplify composing variables in multiple steps

 Makefile                  | 7 ++++++-
 doc/usage/environment.rst | 8 ++++++++
 scripts/env2string.awk    | 6 ++++++
 3 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/Makefile b/Makefile
index 9e44af2ccb1..6315de93506 100644
--- a/Makefile
+++ b/Makefile
@@ -1813,7 +1813,12 @@ ENV_FILE := $(if $(wildcard $(ENV_FILE_BOARD)),$(ENV_FILE_BOARD),$(ENV_FILE_COMM
 quiet_cmd_gen_envp = ENVP    $@
       cmd_gen_envp = \
 	if [ -f "$(ENV_FILE)" ]; then \
-		cat $(ENV_FILE) >$@; \
+		$(CPP) -P $(CFLAGS) -x assembler-with-cpp -D__ASSEMBLY__ \
+			-D__UBOOT_CONFIG__ \
+			-I . -I include \
+			-I $(srctree)/include -include include/config.h \
+			-I$(srctree)/arch/$(ARCH)/include \
+			$(ENV_FILE) -o $@; \
 	else \
 		echo -n >$@ ; \
 	fi
diff --git a/doc/usage/environment.rst b/doc/usage/environment.rst
index 81130d17f85..5df55cdfa8f 100644
--- a/doc/usage/environment.rst
+++ b/doc/usage/environment.rst
@@ -31,6 +31,14 @@ and has an equals sign immediately afterwards. Spaces before the = are not
 permitted. It is a good idea to indent your scripts so that only the 'var='
 appears at the start of a line.
 
+To add additional text to a variable you can use var+=value. This text is
+merged into the variable during the make process and made available as a
+single value to U-Boot.
+
+This file can include C-style comments. Blank lines and multi-line
+variables are supported, and you can use normal C preprocessor directives
+and CONFIG defines from your board config also.
+
 For example, for snapper9260 you would create a text file called
 `board/bluewater/env/snapper9260.env` containing the environment text.
 
diff --git a/scripts/env2string.awk b/scripts/env2string.awk
index f442d3b7c44..9851925d877 100644
--- a/scripts/env2string.awk
+++ b/scripts/env2string.awk
@@ -29,6 +29,12 @@ NF {
 		}
 		var = arr[1]
 		env = arr[2]
+
+		# Deal with +=
+		if (match(var, "(.*)[+]$", var_arr)) {
+			var = var_arr[1]
+			env = vars[var] env
+		}
 	} else {
 		# Change newline to \n
 		env = env "\\n" $0;
-- 
2.33.0.464.g1972c5931b-goog