Shares of Nvidia (NVDA) are up 33 cents, or 2.2%, at $15.15 after JMP Securities’s Alex Gauna today raised his rating on the shares to Market Perform from Market Underperform, writing that there is “mounting evidence that margin and bookings trends have bottomed for the company and are likely to improve rolling forward due to GPU and Tegra market share gains.”

Nvidia is now enjoying steadily improving yields in the 28-nanometer process used for its chips, and it should find “ample” capacity at 28 nanometer going forward, Gauna thinks. Also, “attach rates” for GPUs in PCs is “stable” and might improve this year thanks to the potential gains in Apple’s (AAPL) Mac and in “ultrabook” laptops at the expense of Advanced Micro Devices (AMD), he thinks.

“Although we have not been able to confirm share gains in Apple (MP) platforms through our own checks,” writes Gauna, “we view it as probable given the strength of Kepler and the need for Apple to utilize its compute features to push performance to the next level with key applications such as Final Cut Pro.”

Moreover, Nvidia’s plan to boost revenues for its “Tegra” application processor in phones and tablets by 50% above 2011′s $360 million should be doable, he thinks, based on design wins such as HTC’s (2498TW) “One X” smartphone:

Based on an attractive array of design wins that include flagship phones from HTC, LG, Fujitsu, and ZTE we believe the company could readily hit this target. However, we note that most of these OEM partners are also heavily engaged with Nvidia’s competition, especially Qualcomm (QCOM), which complicates the ability to have a high level of confidence in the company’s outlook.

Gauna’s is the second upbeat note in the last 24 hours. Yesterday morning, Susquehanna Financial’s Chris Caso reiterated a “Positive” rating on the shares, writing that his “checks” suggest Nvidia’s April-ending fiscal Q1 is on track to meet expectations for $916 million in revenue and 9 cents a share in profit.

The July quarter may be brighter, wrote Caso, depending on how fast Nvidia gets its new “Kepler” GPU to channel partners:

1Q is of course being constrained by Kepler availability as noted on NVDA’s earnings call. Our checks did, however, reveal more optimism for 2Q, mainly driven by better HDD availability, particularly within the desktop segment […] Our conversations with NVDA channel partners indicate that they have thus far gotten no Kepler product as of yet due to the supply shortages discussed on the company’s February call (all Kepler has gone to OEM customers). The channel is hopeful to receive Kepler product in late April/early May, which would suggest improving availability and serve as a tailwind to the GPU business.