[PATCH] hwmon: (jc42) Restore the min/max/critical temperatures on resume

[Martin Blumenstingl <martin.blumenstingl@googlemail.com>]

The JC42 compatible thermal sensor on Kingston KSM32ES8/16ME DIMMs
(using Micron E-Die) is an ST Microelectronics STTS2004 (manufacturer
0x104a, device 0x2201). It does not keep the previously programmed
minimum, maximum and critical temperatures after system suspend and
resume (which is a shutdown / startup cycle for the JC42 temperature
sensor). This results in an alarm on system resume because the hardware
default for these values is 0°C (so any environment temperature greater
than 0°C will trigger the alarm).

Example before system suspend:
  jc42-i2c-0-1a
  Adapter: SMBus PIIX4 adapter port 0 at 0b00
  temp1:        +34.8°C  (low  =  +0.0°C)
                         (high = +85.0°C, hyst = +85.0°C)
                         (crit = +95.0°C, hyst = +95.0°C)

Example after system resume (without this change):
  jc42-i2c-0-1a
  Adapter: SMBus PIIX4 adapter port 0 at 0b00
  temp1:        +34.8°C  (low  =  +0.0°C)             ALARM (HIGH, CRIT)
                         (high =  +0.0°C, hyst =  +0.0°C)
                         (crit =  +0.0°C, hyst =  +0.0°C)

Apply the previously read or previously programmed temperature limits on
system resume. This fixes the alarm due to the hardware defaults of 0°C
because the previously applied limits (from a userspace setting) are
re-applied on system resume.

Fixes: 175c490c9e7f ("hwmon: (jc42) Add support for STTS2004 and AT30TSE004")
Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
---
This is my first change to jc42. I tried to be defensive with applying
the previous values by only configuring them if they are known valid. I
only have this one set of JC42 compatible sensors but I can adapt the
code here based on your suggestions.


 drivers/hwmon/jc42.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/drivers/hwmon/jc42.c b/drivers/hwmon/jc42.c
index 30888feaf589..f98b28ff10ad 100644
--- a/drivers/hwmon/jc42.c
+++ b/drivers/hwmon/jc42.c
@@ -558,6 +558,19 @@ static int jc42_resume(struct device *dev)
 	data->config &= ~JC42_CFG_SHUTDOWN;
 	i2c_smbus_write_word_swapped(data->client, JC42_REG_CONFIG,
 				     data->config);
+
+	if (data->valid || data->temp[t_min])
+		i2c_smbus_write_word_swapped(data->client, temp_regs[t_min],
+					     data->temp[t_min]);
+
+	if (data->valid || data->temp[t_max])
+		i2c_smbus_write_word_swapped(data->client, temp_regs[t_max],
+					     data->temp[t_max]);
+
+	if (data->valid || data->temp[t_crit])
+		i2c_smbus_write_word_swapped(data->client, temp_regs[t_crit],
+					     data->temp[t_crit]);
+
 	return 0;
 }
 
-- 
2.38.1