linux-kernel - [PATCH v4 02/11] hwmon: (amc6821) Make reading and writing fan speed limits consistent

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Message-Id: <20240705213547.1155690-3-linux@roeck-us.net>
Date: Fri,  5 Jul 2024 14:35:38 -0700
From: Guenter Roeck <linux@...ck-us.net>
To: linux-hwmon@...r.kernel.org
Cc: linux-kernel@...r.kernel.org,
	Farouk Bouabid <farouk.bouabid@...rry.de>,
	Quentin Schulz <quentin.schulz@...rry.de>,
	Guenter Roeck <linux@...ck-us.net>
Subject: [PATCH v4 02/11] hwmon: (amc6821) Make reading and writing fan speed limits consistent

The default value of the maximum fan speed limit register is 0,
essentially translating to an unlimited fan speed. When reading
the limit, a value of 0 is reported in this case. However, writing
a value of 0 results in writing a value of 0xffff into the register,
which is inconsistent.

To solve the problem, permit writing a limit of 0 for the maximim fan
speed, effectively translating to "no limit". Write 0 into the register
if a limit value of 0 is written. Otherwise limit the range to
<1..6000000> and write 1..0xffff into the register. This ensures that
reading and writing from and to a limit register return the same value
while at the same time not changing reported values when reading the
speed or limits.

While at it, restrict fan limit writes to non-negative numbers; writing
a negative limit does not make sense and should be reported instead of
being corrected.

Reviewed-by: Quentin Schulz <quentin.schulz@...rry.de>
Signed-off-by: Guenter Roeck <linux@...ck-us.net>
---
v4: No change

v3: Add Quentin's Reviewed-by: tag

v2: Do not accept negative fan speed values
    Display fan speed and speed limit as 0 if register value is 0
    (instead of 6000000), as in original code.
    Only permit writing 0 (unlimited) for the maximum fan speed.

 drivers/hwmon/amc6821.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/drivers/hwmon/amc6821.c b/drivers/hwmon/amc6821.c
index dc35e9b21f91..8e3cc33d8073 100644
--- a/drivers/hwmon/amc6821.c
+++ b/drivers/hwmon/amc6821.c
@@ -616,15 +616,20 @@ static ssize_t fan_store(struct device *dev, struct device_attribute *attr,
 {
 	struct amc6821_data *data = dev_get_drvdata(dev);
 	struct i2c_client *client = data->client;
-	long val;
+	unsigned long val;
 	int ix = to_sensor_dev_attr(attr)->index;
-	int ret = kstrtol(buf, 10, &val);
+	int ret = kstrtoul(buf, 10, &val);
 	if (ret)
 		return ret;
-	val = 1 > val ? 0xFFFF : 6000000/val;
+
+	/* The minimum fan speed must not be unlimited (0) */
+	if (ix == IDX_FAN1_MIN && !val)
+		return -EINVAL;
+
+	val = val > 0 ? 6000000 / clamp_val(val, 1, 6000000) : 0;

 	mutex_lock(&data->update_lock);
-	data->fan[ix] = (u16) clamp_val(val, 1, 0xFFFF);
+	data->fan[ix] = clamp_val(val, 0, 0xFFFF);
 	if (i2c_smbus_write_byte_data(client, fan_reg_low[ix],
 			data->fan[ix] & 0xFF)) {
 		dev_err(&client->dev, "Register write error, aborting.\n");
-- 
2.39.2