linux-kernel - [PATCH 2/2] hwmon: (adt7475) Fix setting of hysteresis registers

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Date:   Mon, 20 Feb 2023 12:29:56 +1300
From:   Tony O'Brien <tony.obrien@...iedtelesis.co.nz>
To:     jdelvare@...e.com, linux@...ck-us.net, linux-hwmon@...r.kernel.org
Cc:     chris.packham@...iedtelesis.co.nz, hdegoede@...hat.com,
        jordan.crouse@....com, linux-kernel@...r.kernel.org
Subject: [PATCH 2/2] hwmon: (adt7475) Fix setting of hysteresis registers

In temp_store(), for the hysteresis setting calculation there were two
errors.  The first tries to clamp the hysteresis value by comparing the
required hysteresis value to THERM - 15C.  This is incorrect since the
hysteresis value is a relative value whereas THERM - 15C is an absolute
value. This causes it to always select 15C for hysteresis.  Change the
first parameter to THERM - val to compare two absolute temperatures.
The second error masks the wrong bits in the hysteresis register; indices
0 and 2 should zero bits [7:4] and preserve bits [3:0], and index 1 should
zero bits [3:0] and preserve bits [7:4].

Fixes: 1c301fc5394f ("hwmon: Add a driver for the ADT7475 hardware monitoring chip")
Signed-off-by: Tony O'Brien <tony.obrien@...iedtelesis.co.nz>
---
 drivers/hwmon/adt7475.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/hwmon/adt7475.c b/drivers/hwmon/adt7475.c
index 77222c35a38e..68233191798e 100644
--- a/drivers/hwmon/adt7475.c
+++ b/drivers/hwmon/adt7475.c
@@ -484,14 +484,14 @@ static ssize_t temp_store(struct device *dev, struct device_attribute *attr,
 		adt7475_read_hystersis(client);
 
 		temp = reg2temp(data, data->temp[THERM][sattr->index]);
-		val = clamp_val(val, temp - 15000, temp);
+		val = clamp_val(temp - val, temp - 15000, temp);
 		val = (temp - val) / 1000;
 
 		if (sattr->index != 1) {
-			data->temp[HYSTERSIS][sattr->index] &= 0xF0;
+			data->temp[HYSTERSIS][sattr->index] &= 0x0F;
 			data->temp[HYSTERSIS][sattr->index] |= (val & 0xF) << 4;
 		} else {
-			data->temp[HYSTERSIS][sattr->index] &= 0x0F;
+			data->temp[HYSTERSIS][sattr->index] &= 0xF0;
 			data->temp[HYSTERSIS][sattr->index] |= (val & 0xF);
 		}
 
-- 
2.39.2