Chad Versace of Intel has published a set of nineteen patches to the Mesa mailing list that implement HiZ and depth resolve support for the Intel Linux graphics driver. Unfortunately, it's not without some regressions.
While the patches are there for hierarchical Z (HiZ) support on Intel hardware, the feature isn't enabled by default as it can result in some Piglit regresssions and problems with mip-mapped depth textures.
The patches add nearly 1,000 lines of code to the Intel Mesa DRI driver, but hopefully the issues will be worked out soon and then turned on by default. See this patch set
if you're interested in giving it a shot.