You installed the Grid Infrastructure using the silent software-only option:

./runInstaller -silent -force -responseFile $HOME/grid.rsp

 
When you try to create the ASM instance and a diskgroup, the asmca command fails with:

Error while detecting Oracle Grid Infrastructure. 
ASMCA needs Oracle Grid Infrastructure to configure ASM.

 
This is because the CRS components still need to be configured, you can do this as the root user as follows:

[root@localhost ~]# $ORACLE_HOME/perl/bin/perl -I \
  $ORACLE_HOME/perl/lib -I \
  $ORACLE_HOME/crs/install $ORACLE_HOME/crs/install/roothas.pl
Using configuration parameter file: /u01/app/11.2.0/grid/crs/install/crsconfig_params
Creating trace directory
LOCAL ADD MODE 
Creating OCR keys for user 'oracle', privgrp 'oinstall'..
Operation successful.
LOCAL ONLY MODE 
Successfully accumulated necessary OCR keys.
Creating OCR keys for user 'root', privgrp 'root'..
Operation successful.
CRS-4664: Node localhost successfully pinned.
Adding Clusterware entries to upstart

localhost     2013/01/10 15:06:48     /u01/app/11.2.0/grid/cdata/localhost/backup_20130110_150648.olr
Successfully configured Oracle Grid Infrastructure for a Standalone Server

 
Once this is done, the asmca command can be run successfully.