tree aa666ca464fa45bea315261b6b0e7081f286aff0
parent 8ca4c447c6165767cdb9493c26f3cea6c0079a92
author Rupert Swarbrick <rswarbrick@lowrisc.org> 1618587113 +0100
committer Rupert Swarbrick <rswarbrick@gmail.com> 1618759908 +0100

[clkmgr] Avoid generating unused root-gated clocks

In top_earlgrey, the "io" clock is only used for feeding clock
dividers and its gated version ("clk_io_root") is unused. Teach
topgen.py to be more careful when constructing rg_srcs, so that it
only adds a clock name if that clock is either exposed in clocks_o or
really is a source for some other clock.

While getting my head around the code, I also rejigged things a bit to
make them easier to understand (and easier to construct
"rg_srcs_set"), adding some comments about what the different
dictionaries mean.

Signed-off-by: Rupert Swarbrick <rswarbrick@lowrisc.org>