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SubjectRe: [PATCH] regulator: qcom_spmi: Fix math of spmi_regulator_set_voltage_time_sel
On Wed 19 Jun 11:56 PDT 2019, Jeffrey Hugo wrote:

> spmi_regulator_set_voltage_time_sel() calculates the amount of delay
> needed as the result of setting a new voltage. Essentially this is the
> absolute difference of the old and new voltages, divided by the slew rate.
>
> The implementation of spmi_regulator_set_voltage_time_sel() is wrong.
>
> It attempts to calculate the difference in voltages by using the
> difference in selectors and multiplying by the voltage step between
> selectors. This ignores the possibility that the old and new selectors
> might be from different ranges, which have different step values. Also,
> the difference between the selectors may encapsulate N ranges inbetween,
> so a summation of each selector change from old to new would be needed.
>
> Lets avoid all of that complexity, and just get the actual voltage
> represented by both the old and new selector, and use those to directly
> compute the voltage delta. This is more straight forward, and has the
> side benifit of avoiding issues with regulator implementations that don't
> have hardware register support to get the current configured range.
>
> Fixes: e92a4047419c ("regulator: Add QCOM SPMI regulator driver")
> Reported-by: Bjorn Andersson <bjorn.andersson@linaro.org>
> Reported-by: Jorge Ramirez-Ortiz <jorge.ramirez-ortiz@linaro.org>
> Signed-off-by: Jeffrey Hugo <jeffrey.l.hugo@gmail.com>

Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>

> ---
> drivers/regulator/qcom_spmi-regulator.c | 8 ++------
> 1 file changed, 2 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/regulator/qcom_spmi-regulator.c b/drivers/regulator/qcom_spmi-regulator.c
> index 13f83be50076..877df33e0246 100644
> --- a/drivers/regulator/qcom_spmi-regulator.c
> +++ b/drivers/regulator/qcom_spmi-regulator.c
> @@ -813,14 +813,10 @@ static int spmi_regulator_set_voltage_time_sel(struct regulator_dev *rdev,
> unsigned int old_selector, unsigned int new_selector)
> {
> struct spmi_regulator *vreg = rdev_get_drvdata(rdev);
> - const struct spmi_voltage_range *range;
> int diff_uV;
>
> - range = spmi_regulator_find_range(vreg);
> - if (!range)
> - return -EINVAL;
> -
> - diff_uV = abs(new_selector - old_selector) * range->step_uV;
> + diff_uV = abs(spmi_regulator_common_list_voltage(rdev, new_selector) -
> + spmi_regulator_common_list_voltage(rdev, old_selector));
>
> return DIV_ROUND_UP(diff_uV, vreg->slew_rate);
> }
> --
> 2.17.1
>

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