cmd: mem: add command for getting ram size for use in scripts

Add a command for getting detected ram size with possibility to
assign it to an environment variable.

example usage:

BPI-R4> memsize
4096 MiB
BPI-R4> memsize memsz
BPI-R4> printenv memsz
memsz=4096
BPI-R4>

board with 8GB ram:

BPI-R4> memsize
8192 MiB
BPI-R4> memsize memsz
BPI-R4> printenv memsz
memsz=8192
BPI-R4>

Signed-off-by: Frank Wunderlich <frank-w@public-files.de>

cmd/Kconfig

@@ -940,6 +940,13 @@ config CMD_MEMINFO_MAP
 
 	  See doc/usage/cmd/meminfo.rst for more information.
 
+config CMD_MEMSIZE
+	bool "memsize"
+	depends on CMD_MEMINFO
+	help
+	  Get RAM via command for use in scripts. Print or assign decimal value
+	  in MiB to environment variable.
+
 config CMD_MEMORY
 	bool "md, mm, nm, mw, cp, cmp, base, loop"
 	default y

cmd/meminfo.c

@@ -8,10 +8,12 @@
 #include <bootstage.h>
 #include <command.h>
 #include <display_options.h>
+#include <env.h>
 #include <lmb.h>
 #include <malloc.h>
 #include <mapmem.h>
 #include <asm/global_data.h>
+#include <linux/sizes.h>
 
 DECLARE_GLOBAL_DATA_PTR;
 
@@ -98,8 +100,31 @@ static int do_meminfo(struct cmd_tbl *cmdtp, int flag, int argc,
 	return 0;
 }
 
+#ifdef CONFIG_CMD_MEMSIZE
+static int do_mem_size(struct cmd_tbl *cmdtp, int flag, int argc,
+		       char *const argv[])
+{
+	u64 memsize = gd->ram_size / SZ_1M;
+
+	if (argc > 1)
+		return env_set_ulong(argv[1], memsize);
+	else
+		printf("%lld MiB\n", memsize);
+
+	return 0;
+}
+#endif /* CONFIG_CMD_MEMSIZE */
+
 U_BOOT_CMD(
 	meminfo,	1,	1,	do_meminfo,
 	"display memory information",
 	""
 );
+
+#ifdef CONFIG_CMD_MEMSIZE
+U_BOOT_CMD(
+	memsize,	2,	1,	do_mem_size,
+	"get detected ram size in MiB, optional set env variable with value",
+	"[envvar]"
+);
+#endif /* CONFIG_CMD_MEMSIZE */