[PATCH v3 2/2] 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 cached values from the JC42_REG_TEMP_UPPER,
JC42_REG_TEMP_LOWER, JC42_REG_TEMP_CRITICAL and JC42_REG_SMBUS (where
the SMBUS register is not related to this issue but a side-effect of
using regcache_sync() during system resume with the previously
cached/programmed values. This fixes the alarm due to the hardware
defaults of 0°C because the previously applied limits (set by userspace)
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>
---
 drivers/hwmon/jc42.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/drivers/hwmon/jc42.c b/drivers/hwmon/jc42.c
index 8d70960d5444..52a60eb0791b 100644
--- a/drivers/hwmon/jc42.c
+++ b/drivers/hwmon/jc42.c
@@ -565,6 +565,10 @@ static int jc42_suspend(struct device *dev)
 
 	data->config |= JC42_CFG_SHUTDOWN;
 	regmap_write(data->regmap, JC42_REG_CONFIG, data->config);
+
+	regcache_cache_only(data->regmap, true);
+	regcache_mark_dirty(data->regmap);
+
 	return 0;
 }
 
@@ -572,9 +576,13 @@ static int jc42_resume(struct device *dev)
 {
 	struct jc42_data *data = dev_get_drvdata(dev);
 
+	regcache_cache_only(data->regmap, false);
+
 	data->config &= ~JC42_CFG_SHUTDOWN;
 	regmap_write(data->regmap, JC42_REG_CONFIG, data->config);
-	return 0;
+
+	/* Restore cached register values to hardware */
+	return regcache_sync(data->regmap);
 }
 
 static const struct dev_pm_ops jc42_dev_pm_ops = {
-- 
2.38.1