Commit 6e07a33f authored by Markus Reichl's avatar Markus Reichl Committed by Greg Kroah-Hartman
Browse files

w1: w1_therm: Add support for Maxim MAX31850 thermoelement IF. 



MAX31850 shares family number 0x3B with DS1825. The device is generally
compatible with DS1825 but needs a different temperature readout.
It operates always in 14 bit mode and has all 4 higher bits of the
Config register set to 1. Conversion time is 100ms.

Signed-off-by: default avatarMarkus Reichl <m.reichl@fivetechno.de>
Link: https://lore.kernel.org/r/20220306145817.8753-1-m.reichl@fivetechno.de


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 6caf745d

drivers/w1/slaves/w1_therm.c

+68 −2
Original line number Diff line number Diff line
@@ -574,6 +574,41 @@ static inline int w1_DS18S20_convert_time(struct w1_slave *sl) 
		return SLAVE_CONV_TIME_OVERRIDE(sl);

}



static inline int w1_DS1825_convert_time(struct w1_slave *sl)

{

	int ret;



	if (!sl->family_data)

		return -ENODEV;	/* device unknown */



	if (SLAVE_CONV_TIME_OVERRIDE(sl) != CONV_TIME_DEFAULT)

		return SLAVE_CONV_TIME_OVERRIDE(sl);



	/* Return the conversion time, depending on resolution,

	 * select maximum conversion time among all compatible devices

	 */

	switch (SLAVE_RESOLUTION(sl)) {

	case 9:

		ret = 95;

		break;

	case 10:

		ret = 190;

		break;

	case 11:

		ret = 375;

		break;

	case 12:

		ret = 750;

		break;

	case 14:

		ret = 100; /* MAX31850 only. Datasheet says 100ms  */

		break;

	default:

		ret = 750;

	}

	return ret;

}



static inline int w1_DS18B20_write_data(struct w1_slave *sl,

				const u8 *data)

{
@@ -594,6 +629,7 @@ static inline int w1_DS18B20_set_resolution(struct w1_slave *sl, int val) 


	/* DS18B20 resolution is 9 to 12 bits */

	/* GX20MH01 resolution is 9 to 14 bits */

	/* MAX31850 resolution is fixed 14 bits */

	if (val < W1_THERM_RESOLUTION_MIN || val > W1_THERM_RESOLUTION_MAX)

		return -EINVAL;
@@ -649,6 +685,7 @@ static inline int w1_DS18B20_get_resolution(struct w1_slave *sl) 
		+ W1_THERM_RESOLUTION_MIN;

	/* GX20MH01 has one special case:

	 *   >=14 means 14 bits when getting resolution from bit value.

	 * MAX31850 delivers fixed 15 and has 14 bits.

	 * Other devices have no more then 12 bits.

	 */

	if (resolution > W1_THERM_RESOLUTION_MAX)
@@ -715,6 +752,34 @@ static inline int w1_DS18S20_convert_temp(u8 rom[9]) 
	return t;

}



/**

 * w1_DS1825_convert_temp() - temperature computation for DS1825

 * @rom: data read from device RAM (8 data bytes + 1 CRC byte)

 *

 * Can be called for any DS1825 compliant device.

 * Is used by MAX31850, too

 *

 * Return: value in millidegrees Celsius.

 */



static inline int w1_DS1825_convert_temp(u8 rom[9])

{

	u16 bv;

	s16 t;



	/* Signed 16-bit value to unsigned, cpu order */

	bv = le16_to_cpup((__le16 *)rom);



	/* Config register bit 7 = 1 - MA31850 found, 14 bit resolution */

	if (rom[4] & 0x80) {

		/* Mask out bits 0 (Fault) and 1 (Reserved) */

		/* Avoid arithmetic shift of signed value */

		bv = (bv & 0xFFFC); /* Degrees, lowest 4 bits are 2^-1, 2^-2 and 2 zero bits */

	}

	t = (s16)bv;	/* Degrees, lowest bit is 2^-4 */

	return (int)t * 1000 / 16;	/* Sign-extend to int; millidegrees */

}



/* Device capability description */

/* GX20MH01 device shares family number and structure with DS18B20 */
@@ -757,9 +822,10 @@ static struct w1_therm_family_converter w1_therm_families[] = { 
		.bulk_read			= false

	},

	{

		/* Also used for MAX31850 */

		.f				= &w1_therm_family_DS1825,

		.convert			= w1_DS18B20_convert_temp,

		.get_conversion_time	= w1_DS18B20_convert_time,

		.convert			= w1_DS1825_convert_temp,

		.get_conversion_time	= w1_DS1825_convert_time,

		.set_resolution		= w1_DS18B20_set_resolution,

		.get_resolution		= w1_DS18B20_get_resolution,

		.write_data			= w1_DS18B20_write_data,