[PATCH] cmd: fdt: Add support for reading stringlist property values

[Marek Vasut <marex@denx.de>]

The fdt command currently handles stringlists as strings in 'fdt get value'
subcommand. Since strings in FDT stringlists are separated by '\0', only
the first value gets inserted into the environment variable passed to the
'fdt get value' command.

Example, consider the following DT snippet:

/ { compatible = "foo", "bar" };

The following command only reports the first string in stringlist:
=> fdt get value var / compatible ; print var
foo

It is not possible to assign list of null-terminated strings into U-Boot
environment variable. Add optional 'index' parameter to the subcommand
'fdt get value <var> <path> <prop> [<index>]' which lets user specify which
string within the stringlist should be assigned into the 'var' variable.
The default value of 'index' is 0 in case it is not present. This way the
'fdt' command API does not change and existing scripts are not broken.

The following command now reports the Nth string in stringlist, counting
from zero:
=> fdt get value var / compatible 1 ; print var
bar

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Cc: Simon Glass <sjg@chromium.org>
Cc: Tom Rini <trini@konsulko.com>
---
 cmd/fdt.c | 34 ++++++++++++++++++++++++++++------
 1 file changed, 28 insertions(+), 6 deletions(-)

diff --git a/cmd/fdt.c b/cmd/fdt.c
index 842e6cb634b..6fbd9205d38 100644
--- a/cmd/fdt.c
+++ b/cmd/fdt.c
@@ -48,11 +48,27 @@ void set_working_fdt_addr(ulong addr)
 /*
  * Get a value from the fdt and format it to be set in the environment
  */
-static int fdt_value_env_set(const void *nodep, int len, const char *var)
+static int fdt_value_env_set(const void *nodep, int len,
+			     const char *var, int index)
 {
-	if (is_printable_string(nodep, len))
-		env_set(var, (void *)nodep);
-	else if (len == 4) {
+	if (is_printable_string(nodep, len)) {
+		const char *nodec = (const char *)nodep;
+		int i;
+
+		/*
+		 * Iterate over all members in stringlist and find the one at
+		 * offset $index. If no such index exists, indicate failure.
+		 */
+		for (i = 0; i < len; i += strlen(nodec) + 1) {
+			if (index-- > 0)
+				continue;
+
+			env_set(var, nodec + i);
+			return 0;
+		}
+
+		return 1;
+	} else if (len == 4) {
 		char buf[11];
 
 		sprintf(buf, "0x%08X", fdt32_to_cpu(*(fdt32_t *)nodep));
@@ -426,10 +442,14 @@ static int do_fdt(struct cmd_tbl *cmdtp, int flag, int argc, char *const argv[])
 				return 0;
 			} else if (nodep && len > 0) {
 				if (subcmd[0] == 'v') {
+					int index = 0;
 					int ret;
 
+					if (argc == 7)
+						index = simple_strtoul(argv[6], NULL, 10);
+
 					ret = fdt_value_env_set(nodep, len,
-								var);
+								var, index);
 					if (ret != 0)
 						return ret;
 				} else if (subcmd[0] == 'a') {
@@ -1085,7 +1105,9 @@ static char fdt_help_text[] =
 	"fdt resize [<extrasize>]            - Resize fdt to size + padding to 4k addr + some optional <extrasize> if needed\n"
 	"fdt print  <path> [<prop>]          - Recursive print starting at <path>\n"
 	"fdt list   <path> [<prop>]          - Print one level starting at <path>\n"
-	"fdt get value <var> <path> <prop>   - Get <property> and store in <var>\n"
+	"fdt get value <var> <path> <prop> [<index>] - Get <property> and store in <var>\n"
+	"                                      In case of stringlist property, use optional <index>\n"
+	"                                      to select string within the stringlist. Default is 0.\n"
 	"fdt get name <var> <path> <index>   - Get name of node <index> and store in <var>\n"
 	"fdt get addr <var> <path> <prop>    - Get start address of <property> and store in <var>\n"
 	"fdt get size <var> <path> [<prop>]  - Get size of [<property>] or num nodes and store in <var>\n"
-- 
2.35.1