linux-kernel - Re: [PATCH 02/10] hwmon: (amc6821) Make reading and writing fan speed limits consistent

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Date: Mon, 1 Jul 2024 13:05:43 +0200
From: Quentin Schulz <quentin.schulz@...rry.de>
To: Guenter Roeck <linux@...ck-us.net>, linux-hwmon@...r.kernel.org
Cc: linux-kernel@...r.kernel.org, Farouk Bouabid <farouk.bouabid@...rry.de>
Subject: Re: [PATCH 02/10] hwmon: (amc6821) Make reading and writing fan speed
 limits consistent

Hi Guenter,

On 6/28/24 5:13 PM, Guenter Roeck wrote:
> 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.
>  > Signed-off-by: Guenter Roeck <linux@...ck-us.net>
> ---
>   drivers/hwmon/amc6821.c | 6 +++---
>   1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/hwmon/amc6821.c b/drivers/hwmon/amc6821.c
> index 3c614a0bd192..e37257ae1a6b 100644
> --- a/drivers/hwmon/amc6821.c
> +++ b/drivers/hwmon/amc6821.c
> @@ -601,7 +601,7 @@ static ssize_t fan_show(struct device *dev, struct device_attribute *devattr,
>   	struct amc6821_data *data = amc6821_update_device(dev);
>   	int ix = to_sensor_dev_attr(devattr)->index;
>   	if (0 == data->fan[ix])
> -		return sprintf(buf, "0");
> +		return sprintf(buf, "6000000");
>   	return sprintf(buf, "%d\n", (int)(6000000 / data->fan[ix]));
>   }
>   
> @@ -625,10 +625,10 @@ static ssize_t fan_store(struct device *dev, struct device_attribute *attr,
>   	int ret = kstrtol(buf, 10, &val);
>   	if (ret)
>   		return ret;
> -	val = 1 > val ? 0xFFFF : 6000000/val;
> +	val = val < 1 ? 0xFFFF : 6000000 / val;
>   
>   	mutex_lock(&data->update_lock);
> -	data->fan[ix] = (u16) clamp_val(val, 1, 0xFFFF);
> +	data->fan[ix] = (u16)clamp_val(val, 0, 0xFFFF);

This is an unrelated change I believe and I would therefore have this in 
its own commit with proper documentation in the commit log. Indeed:

1- Change in fan_show handles the default 0x0 register value (which can 
only currently be achieved via the default value of the registers)
2- Allow (re-)setting unlimited fan speed by allowing the user to pass 
6000001+ instead of clamping it to 6000000 RPM.

Looking good otherwise,
Cheers,
Quentin