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

[Mieczyslaw Nalewaj <namiltd@yahoo.com>]

On 7/30/2026 9:13 PM, Stanislaw Pal wrote:
> 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. Once the autosuspend kicks in, pm_clk gates both clocks
> a few milliseconds after probe has returned.
> 
> That is wrong on two counts:
> 
>   - The clock ops access the CMN PLL registers without taking a runtime
>     PM reference of their own, so any later clk_set_rate() or rate
>     recalculation touches the register file with its bus clock gated.
> 
>   - On IPQ5018 the consequences are not contained to this device:
>     gating the CMN block bus clocks makes the SoC hang on a subsequent
>     bus access. Measured on a TP-Link Archer AX55 v1 (IPQ5018), the
>     machine dies silently within a few milliseconds of the CMN PLL
>     probe returning - mid-character on the UART - and the victim is
>     whichever device happens to probe next. Whether a given boot
>     survives the window is a micro-timing lottery: different binary
>     layouts of the same kernel ranged from occasional failures to a
>     100% reproducible boot loop.
> 
> Keep the runtime PM usage count elevated on the probe success path, so
> the bus clocks stay enabled. With this one change the same board went
> from boot-looping to surviving every boot attempt (verified across
> three previously-failing kernel binaries, plus repeated soft and hard
> resets on the final one).
> 
> Fixes: f81715a4c87c ("clk: qcom: Add CMN PLL clock controller driver for IPQ SoC")
> Cc: stable@vger.kernel.org
> Signed-off-by: Stanislaw Pal <kuncy7@gmail.com>
> ---
Reviewed-by: Mieczyslaw Nalewaj <namiltd@yahoo.com>