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Message-ID: <11250d2d-c8ec-a1dc-2f80-edc531160d3e@roeck-us.net>
Date: Mon, 9 Nov 2020 06:42:45 -0800
From: Guenter Roeck <linux@...ck-us.net>
To: Alexandru Ardelean <ardeleanalex@...il.com>
Cc: Alexandru Ardelean <alexandru.ardelean@...log.com>,
linux-hwmon@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
jdelvare@...e.com, Mark.Thoren@...log.com
Subject: Re: [PATCH 3/3] hwmon: (ltc2945): add support for sense resistor
On 11/8/20 10:41 PM, Alexandru Ardelean wrote:
> On Fri, Nov 6, 2020 at 3:17 PM Guenter Roeck <linux@...ck-us.net> wrote:
>>
>> On Fri, Nov 06, 2020 at 12:18:25PM +0200, Alexandru Ardelean wrote:
>>> The sense resistor is a parameter of the board. It should be configured in
>>> the driver via a device-tree / ACPI property, so that the proper current
>>> measurements can be done in the driver.
>>>
>>> It shouldn't be necessary that userspace need to know about the value of
>>> the resistor. It makes things a bit harder to make the application code
>>> portable from one board to another.
>>>
>>> This change implements support for the sense resistor to be configured from
>>> DT/ACPI and used in current calculations.
>>>
>>
>> This will require a matching deevicetree document.
>
> Ack
> Will create a dt binding schema doc.
> Are you fine with being added as maintainer in the DT doc?
> Seeing as you are the original author of the driver.
>
Sure.
Guenter
>>
>>> Signed-off-by: Alexandru Ardelean <alexandru.ardelean@...log.com>
>>> ---
>>> drivers/hwmon/ltc2945.c | 48 ++++++++++++++++++-----------------------
>>> 1 file changed, 21 insertions(+), 27 deletions(-)
>>>
>>> diff --git a/drivers/hwmon/ltc2945.c b/drivers/hwmon/ltc2945.c
>>> index 75d997d31e01..500401a82c49 100644
>>> --- a/drivers/hwmon/ltc2945.c
>>> +++ b/drivers/hwmon/ltc2945.c
>>> @@ -61,9 +61,11 @@
>>> /**
>>> * struct ltc2945_state - driver instance specific data
>>> * @regmap regmap object to access device registers
>>> + * @r_sense_uohm current sense resistor value
>>> */
>>> struct ltc2945_state {
>>> struct regmap *regmap;
>>> + u32 r_sense_uohm;
>>> };
>>>
>>> static inline bool is_power_reg(u8 reg)
>>> @@ -101,9 +103,8 @@ static long long ltc2945_reg_to_val(struct device *dev, u8 reg)
>>> case LTC2945_MAX_POWER_THRES_H:
>>> case LTC2945_MIN_POWER_THRES_H:
>>> /*
>>> - * Convert to uW by assuming current is measured with
>>> - * an 1mOhm sense resistor, similar to current
>>> - * measurements.
>>> + * Convert to uW by and scale it with the configured
>>> + * sense resistor, similar to current measurements.
>>> * Control register bit 0 selects if voltage at SENSE+/VDD
>>> * or voltage at ADIN is used to measure power.
>>> */
>>> @@ -112,10 +113,10 @@ static long long ltc2945_reg_to_val(struct device *dev, u8 reg)
>>> return ret;
>>> if (control & CONTROL_MULT_SELECT) {
>>> /* 25 mV * 25 uV = 0.625 uV resolution. */
>>> - val *= 625LL;
>>> + val = DIV_ROUND_CLOSEST_ULL(val * 625LL * 1000, st->r_sense_uohm);
>>> } else {
>>> /* 0.5 mV * 25 uV = 0.0125 uV resolution. */
>>> - val = (val * 25LL) >> 1;
>>> + val = DIV_ROUND_CLOSEST_ULL(val * 25LL * 1000, st->r_sense_uohm) >> 1;
>>> }
>>> break;
>>> case LTC2945_VIN_H:
>>> @@ -140,13 +141,10 @@ static long long ltc2945_reg_to_val(struct device *dev, u8 reg)
>>> case LTC2945_MAX_SENSE_THRES_H:
>>> case LTC2945_MIN_SENSE_THRES_H:
>>> /*
>>> - * 25 uV resolution. Convert to current as measured with
>>> - * an 1 mOhm sense resistor, in mA. If a different sense
>>> - * resistor is installed, calculate the actual current by
>>> - * dividing the reported current by the sense resistor value
>>> - * in mOhm.
>>> + * 25 uV resolution. Convert to current and scale it
>>> + * with the value of the sense resistor.
>>> */
>>> - val *= 25;
>>> + val = DIV_ROUND_CLOSEST_ULL(val * 25 * 1000, st->r_sense_uohm);
>>> break;
>>> default:
>>> return -EINVAL;
>>> @@ -169,9 +167,8 @@ static int ltc2945_val_to_reg(struct device *dev, u8 reg,
>>> case LTC2945_MAX_POWER_THRES_H:
>>> case LTC2945_MIN_POWER_THRES_H:
>>> /*
>>> - * Convert to register value by assuming current is measured
>>> - * with an 1mOhm sense resistor, similar to current
>>> - * measurements.
>>> + * Convert to register value, scale it with the configured sense
>>> + * resistor value, similar to current measurements.
>>> * Control register bit 0 selects if voltage at SENSE+/VDD
>>> * or voltage at ADIN is used to measure power, which in turn
>>> * determines register calculations.
>>> @@ -181,14 +178,10 @@ 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_ULL(val, 625);
>>> + val = DIV_ROUND_CLOSEST_ULL(val * 1000, 625 * st->r_sense_uohm);
>>> } else {
>>> - /*
>>> - * 0.5 mV * 25 uV = 0.0125 uV resolution.
>>> - * Divide first to avoid overflow;
>>> - * accept loss of accuracy.
>>> - */
>>> - val = DIV_ROUND_CLOSEST_ULL(val, 25) * 2;
>>> + /* 0.5 mV * 25 uV = 0.0125 uV resolution. */
>>> + val = DIV_ROUND_CLOSEST_ULL(val * 2 * 1000, 25 * st->r_sense_uohm);
>>> }
>>> break;
>>> case LTC2945_VIN_H:
>>> @@ -213,13 +206,10 @@ static int ltc2945_val_to_reg(struct device *dev, u8 reg,
>>> case LTC2945_MAX_SENSE_THRES_H:
>>> case LTC2945_MIN_SENSE_THRES_H:
>>> /*
>>> - * 25 uV resolution. Convert to current as measured with
>>> - * an 1 mOhm sense resistor, in mA. If a different sense
>>> - * resistor is installed, calculate the actual current by
>>> - * dividing the reported current by the sense resistor value
>>> - * in mOhm.
>>> + * 25 uV resolution. Convert to current and scale it
>>> + * with the value of the sense resistor, in mA.
>>> */
>>> - val = DIV_ROUND_CLOSEST_ULL(val, 25);
>>> + val = DIV_ROUND_CLOSEST_ULL(val * 1000, 25 * st->r_sense_uohm);
>>> break;
>>> default:
>>> return -EINVAL;
>>> @@ -475,6 +465,10 @@ static int ltc2945_probe(struct i2c_client *client)
>>> return PTR_ERR(regmap);
>>> }
>>>
>>> + if (device_property_read_u32(dev, "shunt-resistor-micro-ohms",
>>> + &st->r_sense_uohm))
>>> + st->r_sense_uohm = 1000;
>>> +
>>
>> Devicetree could set shunt-resistor-micro-ohms to 0, which would result
>> in divide by 0 errors.
>
> Ack
> Will do a check for this.
>
>>
>> Guenter
>>
>>> st->regmap = regmap;
>>>
>>> /* Clear faults */
>>> --
>>> 2.27.0
>>>
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