xsl sort: using element attribute as sort key!

Hi all,

I am trying to sort based on an elements attribute. Doesn't seem to work.
Can i do this, and if so, what am i doing wrong?
Replies greatly appreciated!

$sort parameter = 'name'
$dir parameter = 'descending'

xml structure:
<dfile>
  <df_data_row>
    <df_data column='name'>Value</df_data>
  </df_data_row>
  <df_data_row>
    <df_data column='phone'>Value2</df_data>
  </df_data_row>
</dfile>

<xsl:if test="$sort">
  <xsl:apply-templates select="dfile/df_data_row">
    <xsl:sort select="df_data/@column = $sort" order="$dir"></xsl:sort>
  </xsl:apply-templates>
</xsl:if>

Cheers,
Adam