I haven't done linseed but my barley I soak over night, then simmer in slow cooker all day. Make sure you put loads of water in as it absorbs it like mad.
You must actually bring linseed to the boil otherwise it is poisonous then simmer for about an hour [or do it in the microwave but be careful] Both linseed and barley tend to burn at the bottom so use a thick based pan ,I use my old pressure cooker