The Lima graphics driver for open-source ARM Mali GPU support on Linux has some performance advantages of ARM Holdings' binary blob, but there's no upstream interest in having the driver mainlined in Mesa.
Last week at XDC2013 there was the state of the open-source ARM GPU drivers. The Lima driver was covered during the presentation by Rob Clark, while in chatting with Luc Verhaegen a few days ago I managed to pick up a couple more details.
Luc expressed that the performance of his Lima driver is "consistently beating the binary" in the range of 6~10% better for GLMark2 and ES2_Gears tests within his Limare driver tests. He also says there's still better performance to be had because under X11 there is no job interleaving right now so he believes there's about 50% performance to be gained by better integration with the display engine and X.Org DDX driver.