Re: [PATCH 4/5] regulator: Support regulators where the voltage selector spans two registers

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] regulator: set_oversize_voltage_sel() clobbers bits outside vsel_mask
--

commit 39998b76249529ca1e99e255be8cd5416b46d9ce
Author: Paul Louvel <paul.louvel@bootlin.com>

regulator: Support regulators where the voltage selector spans two registers

This commit adds the vsel_reg_oversize flag to struct regulator_desc to
support regulators whose voltage selector spans two consecutive 8-bit
registers in little-endian order. It updates the regmap voltage selector
helpers to read and write the two-register selector using regmap bulk
operations.

> diff --git a/drivers/regulator/helpers.c b/drivers/regulator/helpers.c
> index 0def82eb8b46a..1221128dde988 100644
> --- a/drivers/regulator/helpers.c
> +++ b/drivers/regulator/helpers.c
> @@ -118,6 +118,37 @@ static int regulator_range_selector_to_index(struct regulator_dev *rdev,
>  	return -EINVAL;
>  }
>  
> +static int get_voltage_sel_reg(struct regulator_dev *rdev, unsigned int *sel)
> +{
> +	int ret, val_bytes;
> +	unsigned int val;
> +	__le16 buf;
> +
> +	if (rdev->desc->vsel_reg_oversize) {
> +		val_bytes = regmap_get_val_bytes(rdev->regmap);
> +
> +		if (val_bytes != 1)
> +			return -EINVAL;
> +
> +		ret = regmap_bulk_read(rdev->regmap, rdev->desc->vsel_reg, &buf, 2);
> +		if (ret != 0)
> +			return ret;
> +
> +		val = le16_to_cpu(buf);
> +	} else {
> +		ret = regmap_read(rdev->regmap, rdev->desc->vsel_reg, &val);
> +		if (ret != 0)
> +			return ret;
> +	}
> +
> +	val &= rdev->desc->vsel_mask;
> +	val >>= ffs(rdev->desc->vsel_mask) - 1;
> +
> +	*sel = val;
> +
> +	return 0;
> +}

[ ... ]

> @@ -161,6 +189,19 @@ int regulator_get_voltage_sel_pickable_regmap(struct regulator_dev *rdev)
>  }
>  EXPORT_SYMBOL_GPL(regulator_get_voltage_sel_pickable_regmap);
>  
> +static int set_oversize_voltage_sel(struct regulator_dev *rdev, unsigned int sel)
> +{
> +	int val_bytes = regmap_get_val_bytes(rdev->regmap);
> +	__le16 val;
> +
> +	if (val_bytes != 1)
> +		return -EINVAL;
> +
> +	val = cpu_to_le16(sel);
> +
> +	return regmap_bulk_write(rdev->regmap, rdev->desc->vsel_reg, &val, 2);
> +}
> +
>  static int write_separate_vsel_and_range(struct regulator_dev *rdev,
>  					 unsigned int sel, unsigned int range)
>  {
> @@ -173,15 +214,17 @@ static int write_separate_vsel_and_range(struct regulator_dev *rdev,
>  	if (ret)
>  		return ret;
>  
> +	if (rdev->desc->vsel_reg_oversize)
> +		return set_oversize_voltage_sel(rdev, sel);

[Severity: High]
When rdev->desc->vsel_reg_oversize is enabled and rdev->desc->vsel_mask does
not span all 16 bits of the two 8-bit registers, will
set_oversize_voltage_sel() clobber the bits outside vsel_mask in vsel_reg and
vsel_reg + 1?

In get_voltage_sel_reg(), the 16-bit value read across the two registers is
masked and shifted with rdev->desc->vsel_mask, and callers such as
regulator_set_voltage_sel_regmap() shift sel into position before calling
set_oversize_voltage_sel():

drivers/regulator/helpers.c:regulator_set_voltage_sel_regmap() {
	sel <<= ffs(rdev->desc->vsel_mask) - 1;

	if (rdev->desc->vsel_reg_oversize)
		ret = set_oversize_voltage_sel(rdev, sel);
	else
		ret = regmap_update_bits(rdev->regmap, rdev->desc->vsel_reg,
					 rdev->desc->vsel_mask, sel);
}

Unlike the regmap_update_bits() path, set_oversize_voltage_sel() writes the
16-bit value directly with regmap_bulk_write() without reading the current
register values and preserving bits outside rdev->desc->vsel_mask, which will
overwrite any other control or reserved bits in those two registers with
zeroes.

In addition, how does vsel_reg_oversize interact with
regulator_set_voltage_sel_pickable_regmap()?

If vsel_range_reg is vsel_reg + 1 (sharing the second register with the upper
bits of the voltage selector), write_separate_vsel_and_range() first updates
vsel_range_reg via regmap_update_bits_base() and then calls
set_oversize_voltage_sel(), which bulk-writes two bytes starting at vsel_reg
and overwrites the range bits just written to vsel_reg + 1.

Furthermore, if vsel_range_reg equals vsel_reg in
regulator_set_voltage_sel_pickable_regmap():

drivers/regulator/helpers.c:regulator_set_voltage_sel_pickable_regmap() {
    ...
	if (rdev->desc->vsel_reg == rdev->desc->vsel_range_reg)
		ret = regmap_update_bits(rdev->regmap, rdev->desc->vsel_reg,
					 rdev->desc->vsel_range_mask |
					 rdev->desc->vsel_mask, sel | range);
	else
		ret = write_separate_vsel_and_range(rdev, sel, range);
    ...
}

won't this take the single-register regmap_update_bits() branch and drop the
upper byte of the oversized selector?

>[!NOTE]
>Please reply to this email with feedback:
>* Did I find a real bug? If not, what did I get wrong?
>* Did I miss a bug on the lines I commented on?

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Sashiko AI review · https://sashiko.dev/#/patchset/20261021-paul-lm51772-v1-0-25f0ffbffa8d@bootlin.com?part=4