[U-Boot] u-boot environment variable parsing

[Hebbar, Gururaja]

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