[PATCH v2] clk: qcom: ipq-cmn-pll: keep the CMN block bus clocks enabled

The probe function takes a runtime PM reference to enable the GCC AHB &
SYS clocks of the CMN PLL block, registers the clocks, and then drops
the reference, letting pm_clk gate both clocks a few milliseconds after
probe has returned. The clock ops access the CMN PLL registers without
a runtime PM reference of their own, and on IPQ5018 gating the CMN
block bus clocks makes the SoC hang on a subsequent bus access: boards
died silently within milliseconds of the CMN PLL probe, up to a 100%
reproducible boot loop, depending on binary layout (micro-timing).

Take a devres-managed runtime PM reference in probe, so the bus clocks
stay enabled for as long as the driver is bound and the reference is
released again on unbind.

Fixes: f81715a4c87c ("clk: qcom: Add CMN PLL clock controller driver for IPQ SoC")
Cc: [email protected]
Signed-off-by: Stanislaw Pal <[email protected]>
---
Changes in v2:
- Use devm_pm_runtime_get_noresume() instead of simply skipping the
  pm_runtime_put() on the probe success path. The v1 arrangement left
  the usage count elevated with nothing to balance it on unbind; the
  devres action releases it. Spotted by the Sashiko automated review
  (thanks to Mieczyslaw Nalewaj for pointing it out). Note that
  pm_runtime_reinit() on unbind does set the status back to suspended,
  so the leak did not have the re-bind consequences the report
  suggested - but it was a leak nonetheless, and the devres form is
  the idiomatic way to express "keep this device resumed while bound".
- The diff is now purely additive; the existing error handling in
  probe is left untouched.

Note for stable: devm_pm_runtime_get_noresume() was added in v6.16 by
commit 73db799bf5ef ("PM: runtime: Add new devm functions"), while this
driver dates back to v6.14. On 6.14.y/6.15.y (both EOL) the equivalent
is to move the pm_runtime_put() out of probe and add one to
ipq_cmn_pll_clk_remove() instead.

v1: https://lore.kernel.org/linux-clk/[email protected]/

 drivers/clk/qcom/ipq-cmn-pll.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

--- a/drivers/clk/qcom/ipq-cmn-pll.c
+++ b/drivers/clk/qcom/ipq-cmn-pll.c
@@ -437,6 +437,17 @@ static int ipq_cmn_pll_clk_probe(struct
 	if (ret)
 		return ret;

+	/*
+	 * The clock ops access the CMN PLL registers without taking a
+	 * runtime PM reference of their own, and on IPQ5018 gating the CMN
+	 * block AHB & SYS clocks after probe hangs the SoC on a subsequent
+	 * bus access. Hold a reference for as long as the driver is bound
+	 * so that the bus clocks stay enabled.
+	 */
+	ret = devm_pm_runtime_get_noresume(dev);
+	if (ret)
+		return ret;
+
 	/* Register CMN PLL clock and fixed rate output clocks. */
 	ret = ipq_cmn_pll_register_clks(pdev);
 	pm_runtime_put(dev);