Re: [lm-sensors] [PATCH] hwmon: TI TMP121 SPI temperature sensor

[Jean Delvare <khali@linux-fr.org>]

Hi Manuel,

Le lundi 15 septembre 2008, Manuel Lauss a écrit :
> Driver for the Texas Instruments TMP121/TMP123 SPI temperature sensors.
> The code is 99% identical to the LM70 driver;  only the formula to
> calculate the temperature (in 1/1000 deg celsius) has been adjusted.
> 
> Signed-off-by: Manuel Lauss <mano@roarinelk.homelinux.net>
> ---
>  drivers/hwmon/Kconfig  |   10 +++
>  drivers/hwmon/Makefile |    1 +
>  drivers/hwmon/tmp121.c |  168 ++++++++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 179 insertions(+), 0 deletions(-)
>  create mode 100644 drivers/hwmon/tmp121.c

Wouldn't it make more sense to just add support for the TMP121/TMP123
chips to the lm70 driver? Duplicating code is better avoided when
possible. Thankfully these drivers are relatively small, but still...

> --- /dev/null
> +++ b/drivers/hwmon/tmp121.c
> (...)
> +	/*
> +	 * The "raw" temperature read into rxbuf[] is a 16-bit signed 2's
> +	 * complement value. Only the MSB 13 bits (1 sign + 12 temperature
> +	 * bits) are meaningful; the LSB 3 bits are to be discarded.
> +	 * Each bit represents 0.0625 degrees Celsius.
> +	 */
> +	val = (raw * 625) / 80;

This does not actually discard the 3 LSB. In order to do that, you
would need to write the following:

	val = (raw / 8) * 625 / 10;

-- 
Jean Delvare

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