Re: [PATCH v2 10/16] mfd: mt6397-core: add mt6323 thermal support

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:
- [High] The `mtk_pmic_thermal` driver causes a kernel panic (NULL pointer dereference) if instantiated with a malformed device tree that lacks the expected parent hierarchy.
- [High] The `mtk_pmic_thermal` driver aborts probing if the optional `nvmem-cells` device tree property is missing, breaking support for uncalibrated operation and violating its DT binding.
--

commit 3e8b78507795872b5938fe1527d98ac0e8b204df
Author: Roman Vivchar <rva333@protonmail.com>

mfd: mt6397-core: add mt6323 thermal support
    
The mt6323 PMIC temperature can be measured using AUXADC channel.
Register the thermal in the mt6323 devices array to allow the
corresponding driver to probe using compatible string.

> diff --git a/drivers/mfd/mt6397-core.c b/drivers/mfd/mt6397-core.c
> index 2d9419b80a5c3..061ac242f1f8b 100644
> --- a/drivers/mfd/mt6397-core.c
> +++ b/drivers/mfd/mt6397-core.c
> @@ -151,6 +151,9 @@ static const struct mfd_cell mt6323_devs[] = {
>  		.num_resources = ARRAY_SIZE(mt6323_pwrc_resources),
>  		.resources = mt6323_pwrc_resources,
>  		.of_compatible = "mediatek,mt6323-pwrc"
> +	}, {
> +		.name = "mt6323-thermal",
> +		.of_compatible = "mediatek,mt6323-thermal",

Does the mtk_pmic_thermal driver gracefully handle missing device tree
properties when instantiated here?

Looking at mtk_pmic_thermal_get_calib_data():

drivers/thermal/mediatek/mtk_pmic_thermal.c:mtk_pmic_thermal_get_calib_data() {
	...
	cell = nvmem_cell_get(dev, NULL);
	if (IS_ERR(cell))
		return PTR_ERR(cell);
	...
}

If the optional nvmem-cells property is missing, nvmem_cell_get() returns
an error. This causes the driver to unconditionally abort probing, which
prevents it from reaching its intended default calibration fallback.

Can this also cause a kernel panic if instantiated with a device tree that
lacks the expected parent hierarchy?

Looking at mtk_pmic_thermal_probe():

drivers/thermal/mediatek/mtk_pmic_thermal.c:mtk_pmic_thermal_probe() {
	...
	mt->regmap = dev_get_regmap(dev->parent->parent, NULL);
	if (!mt->regmap)
		return dev_err_probe(dev, -ENODEV, "failed to get regmap");
	...
}

If the thermal device is instantiated from a top-level node rather than as
an MFD child, dev->parent points to the platform_bus device. Because
platform_bus.parent is NULL, dev->parent->parent resolves to NULL. Passing
this NULL pointer to dev_get_regmap() triggers a panic when the core
attempts to acquire the devres_lock spinlock.

>  	},
>  };

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260512-mt6323-v2-0-3efcba579e88@protonmail.com?part=10