linux-kernel - Re: [PATCH] dell-smm-hwmon: Cache fan_type() calls and use fan

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Date:	Sun, 29 May 2016 20:27:15 +0100
From:	Peter Saunderson <peteasa@...il.com>
To:	Pali Rohár <pali.rohar@...il.com>,
	Thorsten Leemhuis <fedora@...mhuis.info>
Cc:	Jan C Peters <jcpeters89@...il.com>,
	David Santamaría Rogado <howl.nsp@...il.com>,
	Jean Delvare <jdelvare@...e.com>,
	Guenter Roeck <linux@...ck-us.net>,
	Tolga Cakir <cevelnet@...il.com>, linux-hwmon@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] dell-smm-hwmon: Cache fan_type() calls and use
 fan_status() for fan detection

I have just tested removing i8k_get_fan_type() function from the 
dell-smm-hwmon driver in the kernel on my Dell Inspiron 580 and the fan 
speed problem goes away.  My patch simply replaced fan_type with 
fan_status in i8k_init_hwmon and used the index as the type in 
i8k_hwmon_show_fan_label since index and the type were the same 
numerical value on my machine.

Removing i8k_get_fan_type() function for Dell Inspiron 580 would be a 
very good fix!  Well done for finding it!

On 27/05/16 14:21, Pali Rohár wrote:
> So, once kernel call i8k_get_fan_type() function, then fan speed going
> up/down? Even if it was called only at once? Can you confirm it? Caching
> patch cause that for each fan that function is called exactly one time.
Yes even if the i8k_get_fan_type() function is called once I get the fan 
speed problem.
> If this is problem, we can probably create DMI list of machines which do
> not like i8k_get_fan_type() call and disable it for them.
Please add Dell Inspiron 580 to any blacklist that you create.  The 
DMI_PRODUCT_NAME seems to have a white space at the end:

	{
		/*
		 * CPU fan speed going up and down on Dell Inspiron 580
		 * for unknown reasons.
		 */
		.ident = "Dell Inspiron 580",
		.matches = {
			DMI_EXACT_MATCH(DMI_SYS_VENDOR, "Dell Inc."),
			DMI_EXACT_MATCH(DMI_PRODUCT_NAME, "Inspiron 580 "),
		},
	},