Re: [PATCH] clk: qcom: gcc-ipq5018: mark 'gpll0_main' clock as critical

[Stanislaw Pal <kuncy7@gmail.com>]

Tested-by: Stanislaw Pal <kuncy7@gmail.com>

Tested on the TP-Link Archer AX55 v1, the board named in the commit
message, on OpenWrt main with kernel 6.18.44 and ipq-cmn-pll built in.

The image carries your patch and not the ipq-cmn-pll one, so this is
your fix on its own: devm_pm_runtime_get_noresume() is absent from
ipq_cmn_pll_clk_probe() and the CLK_IS_CRITICAL flag is the only change
against main. The board boots reliably, with no hang and no watchdog
reset.

/sys/kernel/debug/clk/clk_summary shows the flag doing its work:
gpll0_main sits at enable count 3 here, against 2 on an image that keeps
the PLL alive through the ipq-cmn-pll reference instead. The chain you
describe is visible on the hardware as well:

  gcc_cmn_blk_ahb_clk -> pcnoc_bfdcd_clk_src -> gpll0 -> gpll0_main

Once the board is up, gpll0 has four other enabled consumers (USB, QPIC,
MDIO, BLSP AHB) while the CPUs have already moved to a53pll. That
matches the failure being confined to the probe window, when none of
those exist yet and the CPUs still run off GPLL0.

For what it is worth on the scope question: on this board the hang was
reproducible with ipq-cmn-pll alone, which is what my patch addresses,
but I agree the root cause is the one you are fixing here - any driver
that takes and releases a clock early enough can pull the PLL out from
under the CPUs. Happy to see it handled in gcc-ipq5018.