regulator: qcom_spmi: Fix math of spmi_regulator_set_voltage_time_sel [Linux 5.3]

This Linux kernel change "regulator: qcom_spmi: Fix math of spmi_regulator_set_voltage_time_sel" is included in the Linux 5.3 release. This change is authored by Jeffrey Hugo <jeffrey.l.hugo [at] gmail.com> on Wed Jun 19 11:56:36 2019 -0700. The commit for this change in Linux stable tree is 61d7fdc (patch).

regulator: qcom_spmi: Fix math of spmi_regulator_set_voltage_time_sel

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>
Reported-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Jeffrey Hugo <jeffrey.l.hugo@gmail.com>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Tested-by: Jorge Ramirez-Ortiz <jorge.ramirez-ortiz@linaro.org>
Signed-off-by: Mark Brown <broonie@kernel.org>

There are 8 lines of Linux source code added/deleted in this change. Code changes to Linux kernel are as follows.

 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 13f83be..877df33 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);
 }

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