clk/broadcom: Add stub clock node for unimplemented clock sources

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Summary

Add bcm_clk_stub, a minimal fixed-frequency clknode used as a
placeholder for clock sources that are not yet fully modelled (e.g.
gnd, testdebug0/1, pllh_aux on BCM2835).

The stub node reports a fixed frequency supplied at registration time
and rejects any set_freq request that would change it. This allows
the peripheral clock mux to resolve all parent names at clkdom_finit()
time without requiring every source to have a real implementation.

bcm_cprman_clk_data gains a stub_clks array; bcm_cprman_attach
registers stub clocks first so they are available as parents when PLLs
and peripheral clocks are registered.

Signed-off-by: perdixky <[e-mail]>

[mhorne]

Can you use the existing clk_fixed class for these clocks? It seems like it. See sys/dev/clk/clk_fixed.h.

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In D55909#1279250, @mhorne wrote:

Can you use the existing clk_fixed class for these clocks? It seems like it. See sys/dev/clk/clk_fixed.h.

No, these two nodes serve different purposes. clk_fixed calls clknode_init_parent_idx(clk, 0) to initialize the parent clock, while clk_stub uses freq = 0 to indicate that it is a dummy clock.

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Updating D55909: clk/broadcom: Add stub clock node for unimplemented clock sources

[3293789706_qq.com]

Updating D55909: clk/broadcom: Add stub clock node for unimplemented clock sources