On Thu, Nov 17, 2016 at 02:08:41PM -0600, Jared Bents wrote: > On Wed, Nov 16, 2016 at 4:51 PM, Guenter Roeck <[email protected]> wrote: > > On Wed, Nov 16, 2016 at 04:23:53PM -0600, Matt Weber wrote: > >> From: Jared Bents <[email protected]> > >> > >> Converts the unsigned temperature values from the i2c read > >> to be sign extended as defined in the datasheet so that > >> negative temperatures are properly read. > >> > >> Signed-off-by: Jared Bents <[email protected]> > >> Signed-off-by: Matt Weber <[email protected]> > >> --- > >> drivers/hwmon/amc6821.c | 2 +- > >> 1 file changed, 1 insertion(+), 1 deletion(-) > >> > >> diff --git a/drivers/hwmon/amc6821.c b/drivers/hwmon/amc6821.c > >> index 12e851a..d7368f7 100644 > >> --- a/drivers/hwmon/amc6821.c > >> +++ b/drivers/hwmon/amc6821.c > >> @@ -188,7 +188,7 @@ static struct amc6821_data > >> *amc6821_update_device(struct device *dev) > >> !data->valid) { > >> > >> for (i = 0; i < TEMP_IDX_LEN; i++) > >> - data->temp[i] = i2c_smbus_read_byte_data(client, > >> + data->temp[i] = (int8_t) > >> i2c_smbus_read_byte_data(client, > > > > How does that fix anything ? The only difference is that errors reported > > from > > i2c_smbus_read_byte_data() are now capped off and stored as 0xff and no > > longer > > as negative numbers. I don't see how a value of 0xff read from the chip > > would > > now be reported as -1 degrees C; it should be reported as 255 degrees C as > > it > > was all along. What am I missing here ? > > > > A real fix would be to actually check for errors either here or in the show > > function (temp[] < 0 indicates a transfer error), and to use sign_extend() > > to convert the 8-bit reading to a signed value. > > > > Guenter > > > > As stated in the patch note, the amc6821 uses signed numbers for the > temperature values. 0xff is -1 Deg C and 0x80 is -128 Deg C via the > temperature range table in the amc6821 datasheet. This change does > not break any error checking when reading the temperature over the i2c > bus in this driver as this driver does not do any error checking for > the temperature reads to begin with. There are error checks in the > driver but they are for some i2c writes and a few i2c reads for > configuration settings. None of those error checks are affected. > Without this patch, the temperatures that are displayed in /sys/class > when below 0 Deg C are 255 Deg C to 128 Deg C. With the patch, the > temperatures displayed below 0 Deg C are -1 Deg C to -128 Deg C as > expected. > Ah, yes, it is "int8_t", which is extended to a negative number. Sorry, I somehow read it as unsigned.
Please run your patch through checkpatch --strict, fix what it reports, and resubmit. Thanks, Guenter -- To unsubscribe from this list: send the line "unsubscribe linux-hwmon" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
