From mboxrd@z Thu Jan  1 00:00:00 1970
From: Hebbar, Gururaja <gururaja.hebbar@ti.com>
Date: Thu, 21 Jul 2011 13:58:40 +0530
Subject: [U-Boot] u-boot environment variable parsing
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To: u-boot@lists.denx.de

Hi, 

I need one clarification regarding Environment variable declaration & its usage.

#define CONFIG_EXTRA_ENV_SETTINGS \
	"brd_mem=62M\0" \
	"bootargs_defaults=setenv bootargs " \
		"console=${console} " \
		 "mem=${brd_mem}\0" \
	"mmc_args=run bootargs_defaults;" \
		"setenv bootargs $(bootargs) " \
		"root=${mmc_root} " \
		"rootfstype=${mmc_root_fs_type} ip=${ip_method}\0" \
	"nand_args=run bootargs_defaults;" \
		"setenv bootargs ${bootargs} " \
		"root=${nand_root} noinitrd " \
		"rootfstype=${nand_root_fs_type} ip=${ip_method}\0" \

The question here is mmc_args re-uses variable bootargs as $(bootargs) & nand_args re-uses it as ${bootargs}. Note the difference in curly & flower brackets. "run mmc_args" fails for me however nand_args runs properly.

My question is 
1. Which is correct?
2. What is the difference between the two?

I have seen few boards using both methods.

Thanks in advance

Regards
Gururaja