gallium/st: add pipe_context::generate_mipmap()

This patch adds a new interface to support hardware mipmap generation.
PIPE_CAP_GENERATE_MIPMAP is added to allow a driver to specify
if this new interface is supported; if not supported, the state tracker will
fallback to mipmap generation by rendering/texturing.

v2: add PIPE_CAP_GENERATE_MIPMAP to the disabled section for all drivers
v3: add format to the generate_mipmap interface to allow mipmap generation
    using a format other than the resource format
v4: fix return type of trace_context_generate_mipmap()

Reviewed-by: Brian Paul <brianp@vmware.com>
Reviewed-by: Roland Scheidegger <sroland@vmware.com>
Reviewed-by: Jose Fonseca <jfonseca@vmware.com>

src/gallium/docs/source/context.rst

@@ -648,3 +648,14 @@ In addition, normal texture sampling is allowed from the compute
 program: ``bind_sampler_states`` may be used to set up texture
 samplers for the compute stage and ``set_sampler_views`` may
 be used to bind a number of sampler views to it.
+
+Mipmap generation
+^^^^^^^^^^^^^^^^^
+
+If PIPE_CAP_GENERATE_MIPMAP is true, ``generate_mipmap`` can be used
+to generate mipmaps for the specified texture resource.
+It replaces texel image levels base_level+1 through
+last_level for layers range from first_layer through last_layer.
+It returns TRUE if mipmap generation succeeds, otherwise it
+returns FALSE. Mipmap generation may fail when it is not supported
+for particular texture types or formats.

src/gallium/docs/source/screen.rst

@@ -303,6 +303,8 @@ The integer capabilities:
   shader buffers are not supported.
 * ``PIPE_CAP_INVALIDATE_BUFFER``: Whether the use of ``invalidate_resource``
   for buffers is supported.
+* ``PIPE_CAP_GENERATE_MIPMAP``: Indicates whether pipe_context::generate_mipmap
+  is supported.
 
 
 .. _pipe_capf: