linux-kernel - Re: [PATCH v3] i8k: Autodetect maximal fan speed and fan RPM multiplier

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Message-Id: <201412211737.18917@pali>
Date:	Sun, 21 Dec 2014 17:37:18 +0100
From:	Pali Rohár <pali.rohar@...il.com>
To:	Guenter Roeck <linux@...ck-us.net>
Cc:	Arnd Bergmann <arnd@...db.de>,
	"Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org, Valdis.Kletnieks@...edu,
	Steven Honeyman <stevenhoneyman@...il.com>,
	Jean Delvare <jdelvare@...e.de>,
	Gabriele Mazzotta <gabriele.mzt@...il.com>,
	Jochen Eisinger <jochen@...guin-breeder.org>
Subject: Re: [PATCH v3] i8k: Autodetect maximal fan speed and fan RPM multiplier

On Sunday 21 December 2014 13:23:32 Guenter Roeck wrote:
> On 12/21/2014 04:09 AM, Pali Rohár wrote:
> > On Sunday 21 December 2014 12:57:08 Guenter Roeck wrote:
> >>> -#define I8K_FAN_MULT		30
> >>> +#define I8K_FAN_MAX_RPM		30000
> >>> 
> >>>    #define I8K_MAX_TEMP		127
> >>>    
> >>>    #define I8K_FN_NONE		0x00
> >>> 
> >>> @@ -64,7 +66,7 @@ static DEFINE_MUTEX(i8k_mutex);
> >>> 
> >>>    static char bios_version[4];
> >>>    static struct device *i8k_hwmon_dev;
> >>>    static u32 i8k_hwmon_flags;
> >>> 
> >>> -static int i8k_fan_mult;
> >>> +static int i8k_fan_mult = 30;
> >> 
> >> Why did you drop I8K_FAN_MULT ?
> > 
> > Because I think it is not needed anymore... It is used only
> > in one place (there ^). But if you want I can revert it
> > back.
> 
> That is not a reason to drop a define.
> 
> >>>    static int __init i8k_probe(void)
> >>>    {
> >>> 
> >>> +	const struct i8k_config_data *conf;
> >> 
> >> Why did you move this variable declaration ?
> > 
> > Comes from previous version of patches where I moved all
> > variables to start of function. I will revert this change.
> > 
> >>> -		const struct i8k_config_data *conf = id->driver_data;
> >>> +		conf = id->driver_data;
> >>> +		if (fan_mult <= 0 && conf->fan_mult > 0)
> >> 
> >> I still don't see the value in accepting fan_mult < 0
> >> (compeared to == 0).
> > 
> > Ok. What kernel driver should do if user load it with
> > negative parameter? We should not propagate negative value
> > to functions.
> 
> You have multiple options: Ignore it (bad idea ;-), abort
> loading the module with -EINVAL, or make the module parameter
> an unsigned.
> 

And how to make module parameter as unsigned? It is possible?

Code

module_param(fan_mult, unsigned int, 0);

cause compile error:

i8k.c:99:1: error: expected ‘=’, ‘,’, ‘;’, ‘asm’ or ‘__attribute__’ before ‘int’
i8k.c:99:1: error: ‘param_ops_unsigned’ undeclared here (not in a function)

-- 
Pali Rohár
pali.rohar@...il.com

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