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

[Gabor Juhos]

On IPQ5018, the APCS core clock feeds the CPUs. It can use
different clocks as its parent, but during system boot it
utilizes GPLL0.

Under some cicumstances, the 'gpll0_main' clock is getting
disabled during kernel start which results in a system hang
then the hardware watchdog restarts the board after a while.

This can happen when a driver gets a clock in its probe function,
then releases it either directly or by devres cleanup on probe
failure.

For example, since v6.18 the kernel often fails to boot on the
TP-Link Archer AX55 v1 board by using the in-tree dts. In the
failing configuration, the 'ipq-cmn-pll' driver is built into
the kernel and the problem is caused by the pm_runtim_put()
call in the ipq_cmn_pll_clk_probe() function. Due to this call,
runtime pm disables the 'gcc_cmn_blk_ahb_clk' clock asynchronously
which results in disabling 'gpll0_main' as well.

Mark the clock as critical in order to avoid such hangs.

Cc: stable@xxxxxxxxxxxxxxx
Fixes: e3fdbef1bab8 ("clk: qcom: Add Global Clock controller (GCC) driver for IPQ5018")
Signed-off-by: Gabor Juhos <j4g8y7@xxxxxxxxx>
---
Note:
There is a patch [1] awaiting upstream which intends to solve the
problem in the case of the 'ipq-cmn-pll' driver. However the same
hang can be reproduced with several other drivers by triggering a
probe failure in them.

The actual patch aims to solve the root cause.

Link: https://lore.kernel.org/r/20260813093351.178419-1-kuncy7@xxxxxxxxx # [1]
---
 drivers/clk/qcom/gcc-ipq5018.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/clk/qcom/gcc-ipq5018.c b/drivers/clk/qcom/gcc-ipq5018.c
index 594dae3bac4c..46da652956fb 100644
--- a/drivers/clk/qcom/gcc-ipq5018.c
+++ b/drivers/clk/qcom/gcc-ipq5018.c
@@ -68,6 +68,15 @@ static struct clk_alpha_pll gpll0_main = {
 			.parent_data = gcc_xo_data,
 			.num_parents = ARRAY_SIZE(gcc_xo_data),
 			.ops = &clk_alpha_pll_stromer_ops,
+			/*
+			 * During system boot, this PLL feeds the CPUs.
+			 * Mark it as critical to ensure that CCF does
+			 * not disable it, even if there are no active
+			 * consumers. This is needed to avoid a system
+			 * hang caused by turning off the clock driving
+			 * the CPUs.
+			 */
+			.flags = CLK_IS_CRITICAL,
 		},
 	},
 };

---
base-commit: 55981579b27b6541aeeab81c768f248dba0491ac
change-id: 20260917-ipq5018-mark-gpll0_main-critical-f3ba32e1f054

Best regards,
-- 
Gabor Juhos <j4g8y7@xxxxxxxxx>