linux-kernel - Re: 答复: [v2,1/1] hwmon: (nct7904) Add watchdog function

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Date:   Fri, 27 Mar 2020 13:54:16 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     yuechao.zhao(赵越超) 
        <yuechao.zhao@...antech.com.cn>
Cc:     "345351830@...com" <345351830@...com>,
        Jean Delvare <jdelvare@...e.com>,
        "linux-hwmon@...r.kernel.org" <linux-hwmon@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Amy.Shih" <Amy.Shih@...antech.com.tw>,
        "Oakley.Ding" <Oakley.Ding@...antech.com.tw>,
        Jia.Sui(贾睢) <Jia.Sui@...antech.com.cn>,
        shengkui.leng(冷胜魁) 
        <shengkui.leng@...antech.com.cn>,
        Rainbow.Zhang(張玉) 
        <Rainbow.Zhang@...antech.com.cn>
Subject: Re: 答复: [v2,1/1] hwmon: (nct7904) Add watchdog function

On 3/26/20 7:39 PM, yuechao.zhao(赵越超) wrote:
> Hi Guenter
> Thank you very much for the suggestion
> 
> But, I wish to consult you on a few questions.
> The NCT7904 is very special in watchdog function. Its minimum unit is minutes.
> So, what unit do we use for setting the timeout in user space. Minutes or seconds?
> Does the kernel document specify it?
> 
Documentation/watchdog/watchdog-api.rst very clearly specifies that
the timeout is set in seconds.

> Also, about this suggestion:
> 	> +	data->wdt.timeout = timeout * 60; /* in seconds */
> 	> +	data->wdt.min_timeout = 1;
> 	> +	data->wdt.max_timeout = 15300;
> 	Please make it 60 * 255 (or use a respective define) to clarify where the number comes from.
> 
> The reason for not use 60 * 255(or use a respective define ) is that we will set the default timeout with 
> "timeout" parameter when "insmod nct7904.ko".

This is not an argument for
	data->wdt.max_timeout = 15300;
instead of
	data->wdt.max_timeout = 60 * 255;
or

#define MAX_TIMEOUT	(60 * 255)
...
	data->wdt.max_timeout = MAX_TIMEOUT;

> The relevant code as follows:
> 	> +static int timeout = WATCHDOG_TIMEOUT; module_param(timeout, int, 0); 
> 	> +MODULE_PARM_DESC(timeout, "Watchdog timeout in minutes. 1 <= timeout <= 255, default="
> 	> +			__MODULE_STRING(WATCHODOG_TIMEOUT) ".");
> 

I accepted that you want to have a module parameter which specifies
the timeout in minutes instead of seconds (as would be customary).
However, I completely fail to understand what that has to do with
using an unexplained constant of "15300" when setting the maximum
timeout variable instead of "60 * 255" or, as I had suggested, a
define.

Thanks,
Guenter