It's been a while since Wall Street banks recommended anything to do with either gold or gold stocks, but in a surprising reversal, last week one of Wall Street's biggest bulls Credit Suisse said that the time has come to use gold stocks as a risk off diversifier, while seeing material upside for the precious metal.

Here is why CS' global equity strategist Andrew Garthwaite, believes that it is now time to buy gold:

First, according to Garthwaite, the valuation of gold stocks is abnormally cheap on both P/E - trading at a 25% discount to the broader market vs a 30% premium normally, and also cheap on a price-to-book basis relative to the market

Looking at individual stocks, Credit Suisse writes that its "outperform"-rated stocks which screen cheap and have positive earnings revisions are: Newcrest Mining, Newmont, Endeavour Mining, Perseus, Regis Resources, St Barbara, Agnico Eagle Mines, Barrick Gold, Kinross Gold, Yamana Gold

As for the metal itself, the Swiss bank notes that gold is also at the bottom end of its 10-year range against silver or industrial commodities and 20% below its 2011 peak in real terms.

According to the Credit Suisse model, the price of gold is driven by the TIPS yield and the dollar. Why does this matters?

Recently, the gold price has lagged the fall in TIPS yield (should be 5% higher). Looking at TIPS yields, Garthwaite sees little change; the more investors fear an inflation tail risk as they do on the UoM or FOMC data, the more they will likely want to buy inflation protection and the more expensive the TIPS yield becomes.