gallium/docs: Flesh out the distro information.

I'm not sure I picked the best voice here. I might come back to this
later.

src/gallium/docs/source/context.rst

@@ -1,3 +1,5 @@
+.. _context:
+
 Context
 =======
 

src/gallium/docs/source/distro.rst

@@ -10,69 +10,100 @@ Drivers
 Cell
 ^^^^
 
+Simple driver for the IBM Cell architecture. Runs faster than :ref:`softpipe`
+on Cell-based machines.
+
 Failover
 ^^^^^^^^
 
-Deprecated.
+Broken and deprecated.
 
 Intel i915
 ^^^^^^^^^^
 
+Driver for Intel i915 and i945 chipsets.
+
 Intel i965
 ^^^^^^^^^^
 
-Highly experimental.
+Highly experimental driver for Intel i965 chipsets.
 
 Identity
 ^^^^^^^^
 
-Wrapper driver.
+Wrapper driver. The identity driver is a simple skeleton that passes through
+all of its :ref:`Context` and :ref:`Screen` methods to an underlying Context
+and Screen, and as such, it is an excellent starting point for new drivers.
 
 LLVM Softpipe
 ^^^^^^^^^^^^^
 
-nVidia nv30
+A version of :ref:`softpipe` that uses the Low-Level Virtual Machine to
+dynamically generate optimized rasterizing pipelines.
+
+nVidia nvfx
 ^^^^^^^^^^^
 
-nVidia nv40
+Driver for the nVidia nv30 and nv40 families of GPUs.
-^^^^^^^^^^^
 
 nVidia nv50
 ^^^^^^^^^^^
 
+Driver for the nVidia nv50 family of GPUs.
+
 VMWare SVGA
 ^^^^^^^^^^^
 
+Driver for VMWare virtualized guest operating system graphics processing.
+
 ATI r300
 ^^^^^^^^
 
-Testing-quality.
+Driver for the ATI/AMD r300, r400, and r500 families of GPUs.
+
+.. _softpipe:
 
 Softpipe
 ^^^^^^^^
 
-Reference software rasterizer.
+Reference software rasterizer. Slow but accurate.
 
 Trace
 ^^^^^
 
-Wrapper driver.
+Wrapper driver. Trace dumps an XML record of the calls made to the
+:ref:`Context` and :ref:`Screen` objects that it wraps.
 
 State Trackers
 --------------
 
+.. _dri:
+
 Direct Rendering Infrastructure
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
+Tracker that implements the client-side DRI protocol, for providing direct
+acceleration services to X11 servers with the DRI extension. Supports DRI1
+and DRI2. Only GL is supported.
+
+.. _egl:
+
 EGL
 ^^^
 
+Tracker for the Khronos EGL standard, used to set up GL and GLES contexts
+without extra knowledge of the underlying windowing system.
+
 GLX
 ^^^
 
 MesaGL
 ^^^^^^
 
+Tracker implementing a GL state machine. Not usable as a standalone tracker;
+Mesa should be built with another state tracker, such as :ref:`DRI` or
+:ref:`EGL`.
+
 Python
 ^^^^^^
 
@@ -82,9 +113,12 @@ OpenVG
 WGL
 ^^^
 
-Xorg XFree86 DDX
+Xorg/XFree86 DDX
 ^^^^^^^^^^^^^^^^
 
+Tracker for XFree86 and Xorg X11 servers. Provides device-dependent
+modesetting and acceleration as a DDX driver.
+
 Auxiliary
 ---------