net: phy: sfp: Add HWMON support for module sensors

SFP modules can contain a number of sensors. The EEPROM also contains
recommended alarm and critical values for each sensor, and indications
of if these have been exceeded. Export this information via
HWMON. Currently temperature, VCC, bias current, transmit power, and
possibly receiver power is supported.

The sensors in the modules can either return calibrate or uncalibrated
values. Uncalibrated values need to be manipulated, using coefficients
provided in the SFP EEPROM. Uncalibrated receive power values require
floating point maths in order to calibrate them. Performing this in
the kernel is hard. So if the SFP module indicates it uses
uncalibrated values, RX power is not made available.

With this hwmon device, it is possible to view the sensor values using
lm-sensors programs:

in0:          +3.29 V  (crit min =  +2.90 V, min =  +3.00 V)
                       (max =  +3.60 V, crit max =  +3.70 V)
temp1:        +33.0°C  (low  =  -5.0°C, high = +80.0°C)
                       (crit low = -10.0°C, crit = +85.0°C)
power1:      1000.00 nW (max = 794.00 uW, min =  50.00 uW)  ALARM (LCRIT)
                       (lcrit =  40.00 uW, crit = 1000.00 uW)
curr1:        +0.00 A  (crit min =  +0.00 A, min =  +0.00 A)  ALARM (LCRIT, MIN)
                       (max =  +0.01 A, crit max =  +0.01 A)

The scaling sensors performs on the bias current is not particularly
good. The raw values are more useful:

curr1:
  curr1_input: 0.000
  curr1_min: 0.002
  curr1_max: 0.010
  curr1_lcrit: 0.000
  curr1_crit: 0.011
  curr1_min_alarm: 1.000
  curr1_max_alarm: 0.000
  curr1_lcrit_alarm: 1.000
  curr1_crit_alarm: 0.000

In order to keep the I2C overhead to a minimum, the constant values,
such as limits and calibration coefficients are read once at module
insertion time. Thus only reading *_input and *_alarm properties
requires i2c read operations.
Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Acked-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/phy/Kconfig

@@ -215,6 +215,7 @@ config SFP
 	tristate "SFP cage support"
 	depends on I2C && PHYLINK
 	select MDIO_I2C
+	imply HWMON
 
 config AMD_PHY
 	tristate "AMD PHYs"

include/linux/sfp.h

@@ -231,6 +231,50 @@ struct sfp_eeprom_id {
 	struct sfp_eeprom_ext ext;
 } __packed;
 
+struct sfp_diag {
+	__be16 temp_high_alarm;
+	__be16 temp_low_alarm;
+	__be16 temp_high_warn;
+	__be16 temp_low_warn;
+	__be16 volt_high_alarm;
+	__be16 volt_low_alarm;
+	__be16 volt_high_warn;
+	__be16 volt_low_warn;
+	__be16 bias_high_alarm;
+	__be16 bias_low_alarm;
+	__be16 bias_high_warn;
+	__be16 bias_low_warn;
+	__be16 txpwr_high_alarm;
+	__be16 txpwr_low_alarm;
+	__be16 txpwr_high_warn;
+	__be16 txpwr_low_warn;
+	__be16 rxpwr_high_alarm;
+	__be16 rxpwr_low_alarm;
+	__be16 rxpwr_high_warn;
+	__be16 rxpwr_low_warn;
+	__be16 laser_temp_high_alarm;
+	__be16 laser_temp_low_alarm;
+	__be16 laser_temp_high_warn;
+	__be16 laser_temp_low_warn;
+	__be16 tec_cur_high_alarm;
+	__be16 tec_cur_low_alarm;
+	__be16 tec_cur_high_warn;
+	__be16 tec_cur_low_warn;
+	__be32 cal_rxpwr4;
+	__be32 cal_rxpwr3;
+	__be32 cal_rxpwr2;
+	__be32 cal_rxpwr1;
+	__be32 cal_rxpwr0;
+	__be16 cal_txi_slope;
+	__be16 cal_txi_offset;
+	__be16 cal_txpwr_slope;
+	__be16 cal_txpwr_offset;
+	__be16 cal_t_slope;
+	__be16 cal_t_offset;
+	__be16 cal_v_slope;
+	__be16 cal_v_offset;
+} __packed;
+
 /* SFP EEPROM registers */
 enum {
 	SFP_PHYS_ID			= 0x00,
@@ -384,7 +428,33 @@ enum {
 	SFP_TEC_CUR			= 0x6c,
 
 	SFP_STATUS			= 0x6e,
-	SFP_ALARM			= 0x70,
+	SFP_ALARM0			= 0x70,
+	SFP_ALARM0_TEMP_HIGH		= BIT(7),
+	SFP_ALARM0_TEMP_LOW		= BIT(6),
+	SFP_ALARM0_VCC_HIGH		= BIT(5),
+	SFP_ALARM0_VCC_LOW		= BIT(4),
+	SFP_ALARM0_TX_BIAS_HIGH		= BIT(3),
+	SFP_ALARM0_TX_BIAS_LOW		= BIT(2),
+	SFP_ALARM0_TXPWR_HIGH		= BIT(1),
+	SFP_ALARM0_TXPWR_LOW		= BIT(0),
+
+	SFP_ALARM1			= 0x71,
+	SFP_ALARM1_RXPWR_HIGH		= BIT(7),
+	SFP_ALARM1_RXPWR_LOW		= BIT(6),
+
+	SFP_WARN0			= 0x74,
+	SFP_WARN0_TEMP_HIGH		= BIT(7),
+	SFP_WARN0_TEMP_LOW		= BIT(6),
+	SFP_WARN0_VCC_HIGH		= BIT(5),
+	SFP_WARN0_VCC_LOW		= BIT(4),
+	SFP_WARN0_TX_BIAS_HIGH		= BIT(3),
+	SFP_WARN0_TX_BIAS_LOW		= BIT(2),
+	SFP_WARN0_TXPWR_HIGH		= BIT(1),
+	SFP_WARN0_TXPWR_LOW		= BIT(0),
+
+	SFP_WARN1			= 0x75,
+	SFP_WARN1_RXPWR_HIGH		= BIT(7),
+	SFP_WARN1_RXPWR_LOW		= BIT(6),
 
 	SFP_EXT_STATUS			= 0x76,
 	SFP_VSL				= 0x78,