While Fools should generally take the opinion of Wall Street with a grain of salt, it's not a bad idea to take a closer look at particularly stock-shaking analyst upgrades and downgrades -- just in case their reasoning behind the call makes sense.

What: Shares of Marvell Technology Group (NASDAQ:MRVL) gained 2% this morning after Nomura Securities upgraded the chipmaker from neutral to buy.

So what: Along with the upgrade, analyst Sanjay Chaurasia planted a price target of $19 on the stock, representing about 28% worth of upside to yesterday's close. So while momentum traders might be turned off by Marvell's recent price weakness, Chaurasia's call could reflect a sense on Wall Street that the company's market share growth prospects are becoming too cheap to pass up.

Now what: According to Nomura, Marvell's risk/reward trade-off is rather attractive at this point. "We believe the company is ahead of MediaTek in its LTE learning curve," said Chaurasia. "In addition, we believe Marvell is gaining share at Samsung and should disproportionately benefit from Broadcom's recent exit from cellular baseband. While most investors view Marvell's LTE traction as short-lived and expect it to be a repeat of the TDSCDMA story once MediaTek launches its LTE solutions in 2H, we think Marvell's LTE position against MediaTek is stronger than it was with TDSCDMA." More importantly, with Marvell boasting a cash-rich balance sheet and cheapish forward P/E of 12, the downside seems limited enough to bet on that bullishness.