Re: [PATCH v2 2/4] docs: hwmon: (ltc2945): change type of val to ULL in ltc2945_val_to_reg()

Guenter Roeck
2020-11-11T14:54:22Z

On 11/11/20 1:12 AM, Alexandru Ardelean wrote:
> In order to account for any potential overflows that could occur.
>
> Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>

Thinking about it, this can only really happen if the user provides
excessive values for limit attributes. Those are currently clamped
later, after the conversion. I think it would be better to modify
the code to apply a clamp _before_ the conversion as well instead
of trying to solve the overflow problem with unsigned long long.

Either case, can you send me a register dump for this chip ?
I'd like to write a module test script to actually check if there
are any over/underflows or other problems.

Thanks,
Guenter

> ---
> drivers/hwmon/ltc2945.c | 12 ++++++------
> 1 file changed, 6 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/hwmon/ltc2945.c b/drivers/hwmon/ltc2945.c
> index 1cea710df668..6d4569a25471 100644
> --- a/drivers/hwmon/ltc2945.c
> +++ b/drivers/hwmon/ltc2945.c
> @@ -155,7 +155,7 @@ static long long ltc2945_reg_to_val(struct device *dev, u8 reg)
> }
>
> static int ltc2945_val_to_reg(struct device *dev, u8 reg,
> - unsigned long val)
> + unsigned long long val)
> {
> struct ltc2945_state *st = dev_get_drvdata(dev);
> struct regmap *regmap = st->regmap;
> @@ -181,14 +181,14 @@ static int ltc2945_val_to_reg(struct device *dev, u8 reg,
> return ret;
> if (control & CONTROL_MULT_SELECT) {
> /* 25 mV * 25 uV = 0.625 uV resolution. */
> - val = DIV_ROUND_CLOSEST(val, 625);
> + val = DIV_ROUND_CLOSEST_ULL(val, 625);
> } else {
> /*
> * 0.5 mV * 25 uV = 0.0125 uV resolution.
> * Divide first to avoid overflow;
> * accept loss of accuracy.
> */
> - val = DIV_ROUND_CLOSEST(val, 25) * 2;
> + val = DIV_ROUND_CLOSEST_ULL(val, 25) * 2;
> }
> break;
> case LTC2945_VIN_H:
> @@ -197,7 +197,7 @@ static int ltc2945_val_to_reg(struct device *dev, u8 reg,
> case LTC2945_MAX_VIN_THRES_H:
> case LTC2945_MIN_VIN_THRES_H:
> /* 25 mV resolution. */
> - val /= 25;
> + val = div_u64(val, 25);
> break;
> case LTC2945_ADIN_H:
> case LTC2945_MAX_ADIN_H:
> @@ -219,7 +219,7 @@ static int ltc2945_val_to_reg(struct device *dev, u8 reg,
> * dividing the reported current by the sense resistor value
> * in mOhm.
> */
> - val = DIV_ROUND_CLOSEST(val, 25);
> + val = DIV_ROUND_CLOSEST_ULL(val, 25);
> break;
> default:
> return -EINVAL;
> @@ -247,7 +247,7 @@ static ssize_t ltc2945_value_store(struct device *dev,
> struct ltc2945_state *st = dev_get_drvdata(dev);
> struct regmap *regmap = st->regmap;
> u8 reg = attr->index;
> - unsigned long val;
> + unsigned long long val;
> u8 regbuf[3];
> int num_regs;
> int regval;
>