Defining grid extent for HexTile plots

The matplotlib hexbin plot offers the possibility to define the grid size and granularity with the combination of the parameters extent and gridsize. While the parameter gridsize also exists in the HoloViews interface of HexTiles, I was unable to identify the equivalent to extent (for both, matplotlib and bokeh backends). The corresponding values seem to always be automatically calculated from the data.
Can this really not be configured, or did I just miss the right parameter/option?