Re: [PATCH 1/2] pmdomain/rockchip: skip QoS operations for idle-only domains

From: Daniel Bozeman <daniel@orb.net>
To: shawn.lin@rock-chips.com, ulf.hansson@linaro.org,
	heiko@sntech.de, linux-pm@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-rockchip@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/2] pmdomain/rockchip: skip QoS operations for idle-only domains
Date: Wed, 1 Apr 2026 06:13:12 +0000	[thread overview]
Message-ID: <acy3eP0dZBx6A950@claude-dev> (raw)
In-Reply-To: <fc6f00fa-10b0-44c8-d8b4-694f8ff3b9ea@rock-chips.com>

<fc6f00fa-10b0-44c8-d8b4-694f8ff3b9ea@rock-chips.com>

I ran additional tests to gather evidence:

Test 1: Patch 2 only (skip EPROBE_DEFER), no patch 1.
Result: kernel panic. The idle-only domains register
successfully, but genpd_power_off_work_fn attempts to power
them off and crashes in rockchip_pmu_set_idle_request:

  Internal error: synchronous external abort: 0000000096000010
  CPU: 0 PID: 59 Comm: kworker/0:3
  Workqueue: pm genpd_power_off_work_fn
  pc : regmap_mmio_read32le+0x8/0x20
  Call trace:
   regmap_mmio_read32le+0x8/0x20
   _regmap_bus_reg_read+0x6c/0xac
   _regmap_read+0x60/0xd8
   regmap_read+0x4c/0x7c
   rockchip_pmu_set_idle_request.isra.0+0x94/0x1b4
   rockchip_pd_power+0x378/0x604
   rockchip_pd_power_off+0x14/0x34
   genpd_power_off.isra.0+0x1f0/0x2f0
   genpd_power_off_work_fn+0x34/0x54

Test 2: No kernel patches, PD_GPU disabled via
status = "disabled" in DTS to avoid EPROBE_DEFER entirely.
Result: same kernel panic. The idle-only domains register
but crash identically when genpd tries to power them off.
Same call trace as above.

So the crash is not caused by probe ordering or
EPROBE_DEFER -- it happens whenever idle-only domains
(pwr_mask == 0) are registered and genpd attempts to
power them off. The QoS register access in
rockchip_pmu_set_idle_request faults on these domains.

Regarding S2R: you raise a valid concern about skipping
QoS save/restore. However, these idle-only domains cannot
actually be powered off (pwr_mask == 0), so
rockchip_do_pmu_set_power_domain already returns early for
them. The QoS save/idle/restore cycle in rockchip_pd_power
has no effect on these domains since the power state never
changes -- the save and restore are paired around a no-op.
Skipping the entire sequence for pwr_mask == 0 should be
safe for S2R as well.

Both patches are needed:
- Patch 1: prevents the QoS crash on idle-only domains
- Patch 2: prevents probe teardown from making things worse

Tested on NanoPi Zero2 (RK3528) with all four scenarios:
both patches (boots), patch 2 only (panic), DTS workaround
(panic), both patches + E20C regression test (no issues).

The board DTS that triggers this (GPIO-controlled USB VBUS
regulator on GPIO4/PD_RKVENC) can be seen at:
https://github.com/dboze/openwrt/blob/add-nanopi-zero2-clean/target/linux/rockchip/patches-6.12/102-arm64-dts-rockchip-Add-FriendlyElec-NanoPi-Zero2.patch