Re: [PATCH] drm/msm/dsi: fix AHB clock staying enabled across suspend

[Joonhoe Kim]

(Resending with the lists on Cc; my earlier reply only went to Arpit.)

On Tue, Oct 06, 2026 at 06:43:53PM +0530, Arpit Saini wrote:
> pm_clk_suspend()/resume() only call clk_disable()/clk_enable() for the
> AHB ("iface") clock, never clk_unprepare(), so prepare_count never
> reaches 0. The clock (and its source) stays reported as enabled
> through s2idle suspend even though the display stack is fully
> suspended:

I looked at this on a Lenovo Legion Tab Y700 Gen 5 (SM8850, bonded DSI,
v7.3-rc4), comparing the current code, this patch's approach, and
preparing the clock only in the PHY runtime callbacks.

In s2idle with the display on I see no difference: in all three cases
both PHYs are already runtime suspended at system suspend,
disp_cc_mdss_ahb_clk has enable_count 0, and CX collapse during a 100 s
s2idle is the same. Is the clock really enabled during suspend on your
board, or only prepared? Reading clk_summary runtime-resumes the clock
controllers, so it can show a different state.

The difference here is with the display off and the system awake: with
the clock prepared from probe (current code and this patch), dispcc
stays runtime active and MMCX stays on. Preparing it in the runtime
callbacks lets both go off. I have not measured the power difference.

That variant survived 30 DPMS off/on cycles with clk_summary read in a
loop. Did you hit the prepare_lock deadlock, or is it from code
reading?

Thanks,
Joonhoe Kim