Re: [v3,1/3] hwmon: ltc2990: refactor value conversion

[Tom Levens]

On Sat, 8 Jul 2017, Guenter Roeck wrote:

> On Mon, Jul 03, 2017 at 06:28:58AM +0200, Tom Levens wrote:
> > Conversion from raw values to signed integers has been refactored using
> > bitops.h. This also fixes a bug where negative temperatures were
> > converted incorrectly.
>
> Documentation/process/submitting-patches.rst, chapter 2: "Solve only one
> problem per patch.".
>
> I can understand the urge to merge two sets of changes here. However,
> that creates a problem for me: The fix should be applied to stable kernels,
> but not the refactoring.
>
> Please split the patch in two, one for the bug fix and one for the
> refactoring.

In reality the refactoring *is* the fix for this bug. I am not sure how to 
to fix it simply without using the bitops macro. Of course, I could fix 
only the temperature conversion in one patch and refactor the other two in 
a separate one if you prefer?

Cheers,

> Thanks,
> Guenter
>
> > Signed-off-by: Tom Levens <tom.levens@xxxxxxx>
> > ---
> >  drivers/hwmon/ltc2990.c | 18 ++++--------------
> >  1 file changed, 4 insertions(+), 14 deletions(-)
> >
> > diff --git a/drivers/hwmon/ltc2990.c b/drivers/hwmon/ltc2990.c
> > index 8f8fe05..e320d21 100644
> > --- a/drivers/hwmon/ltc2990.c
> > +++ b/drivers/hwmon/ltc2990.c
> > @@ -11,6 +11,7 @@
> >   * the chip's internal temperature and Vcc power supply voltage.
> >   */
> >
> > +#include <linux/bitops.h>
> >  #include <linux/err.h>
> >  #include <linux/hwmon.h>
> >  #include <linux/hwmon-sysfs.h>
> > @@ -34,15 +35,6 @@
> >  #define LTC2990_CONTROL_MODE_CURRENT	0x06
> >  #define LTC2990_CONTROL_MODE_VOLTAGE	0x07
> >
> > -/* convert raw register value to sign-extended integer in 16-bit range */
> > -static int ltc2990_voltage_to_int(int raw)
> > -{
> > -	if (raw & BIT(14))
> > -		return -(0x4000 - (raw & 0x3FFF)) << 2;
> > -	else
> > -		return (raw & 0x3FFF) << 2;
> > -}
> > -
> >  /* Return the converted value from the given register in uV or mC */
> >  static int ltc2990_get_value(struct i2c_client *i2c, u8 reg, int *result)
> >  {
> > @@ -55,18 +47,16 @@ static int ltc2990_get_value(struct i2c_client *i2c, u8 reg, int *result)
> >  	switch (reg) {
> >  	case LTC2990_TINT_MSB:
> >  		/* internal temp, 0.0625 degrees/LSB, 13-bit  */
> > -		val = (val & 0x1FFF) << 3;
> > -		*result = (val * 1000) >> 7;
> > +		*result = sign_extend32(val, 12) * 1000 / 16;
> >  		break;
> >  	case LTC2990_V1_MSB:
> >  	case LTC2990_V3_MSB:
> >  		 /* Vx-Vy, 19.42uV/LSB. Depends on mode. */
> > -		*result = ltc2990_voltage_to_int(val) * 1942 / (4 * 100);
> > +		*result = sign_extend32(val, 14) * 1942 / 100;
> >  		break;
> >  	case LTC2990_VCC_MSB:
> >  		/* Vcc, 305.18ÎV/LSB, 2.5V offset */
> > -		*result = (ltc2990_voltage_to_int(val) * 30518 /
> > -			   (4 * 100 * 1000)) + 2500;
> > +		*result = sign_extend32(val, 14) * 30518 / (100 * 1000) + 2500;
> >  		break;
> >  	default:
> >  		return -EINVAL; /* won't happen, keep compiler happy */