dell-smm-hwmon: Cache fan_type() calls and use fan_status() for fan detection

Commit Message

Thorsten Leemhuis May 30, 2016, 11:45 a.m. UTC

Pali Rohár wrote on 27.05.2016 15:21:
> On Friday 27 May 2016 15:05:54 Thorsten Leemhuis wrote:
>> Pali Rohár wrote on 27.05.2016 12:45:
>> So I tried a few things
>> and came to the conclusion: the problem shows up as soon as
>> i8k_get_fan_type() (introduced in f989e55452) is called somewhere.
> So, once kernel call i8k_get_fan_type() function, then fan speed going 
> up/down?

Yes.

> To make sure that this is root of your problem, can you take some older 
> kernel version (where is i8k working fine) and try to patch+call that 
> i8k_get_fan_type() function? To check that something else cannot 
> interference with it...

I just tried with 3.19.8 (had to install a older distro first :-/ ),
where the problem does not show up (I verified just to be sure). Then I
applied below patch and voila: the fan speed starts going up/down.

IOW: From what I can see that SMM call that i8k_get_fan_type() triggers
the problem on my Studio 8000

CU, knurd

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Comments

Pali Rohár June 13, 2016, 6:30 p.m. UTC | #1

On Monday 30 May 2016 13:45:51 Thorsten Leemhuis wrote:
> Pali Rohár wrote on 27.05.2016 15:21:
> > On Friday 27 May 2016 15:05:54 Thorsten Leemhuis wrote:
> >> Pali Rohár wrote on 27.05.2016 12:45:
> >> So I tried a few things
> >> and came to the conclusion: the problem shows up as soon as
> >> i8k_get_fan_type() (introduced in f989e55452) is called somewhere.
> > 
> > So, once kernel call i8k_get_fan_type() function, then fan speed
> > going up/down?
> 
> Yes.
> 
> > To make sure that this is root of your problem, can you take some
> > older kernel version (where is i8k working fine) and try to
> > patch+call that i8k_get_fan_type() function? To check that
> > something else cannot interference with it...
> 
> I just tried with 3.19.8 (had to install a older distro first :-/ ),
> where the problem does not show up (I verified just to be sure). Then
> I applied below patch and voila: the fan speed starts going up/down.
> 
> IOW: From what I can see that SMM call that i8k_get_fan_type()
> triggers the problem on my Studio 8000
> 
> CU, knurd
> 

Thank you for your testing! I believe now we definitely know root of 
this problem. It is buggy Dell BIOS/SMM code and we need to avoid 
calling I8K_SMM_GET_FAN_TYPE on affected buggy Dell machines.

Patch

--- i8k.c-unmodified	2016-05-30 13:04:32.980825405 +0200
+++ i8k.c	2016-05-30 13:25:03.186630115 +0200
@@ -41,6 +41,7 @@ 
 #define I8K_SMM_SET_FAN		0x01a3
 #define I8K_SMM_GET_FAN		0x00a3
 #define I8K_SMM_GET_SPEED	0x02a3
+#define I8K_SMM_GET_FAN_TYPE   0x03a3
 #define I8K_SMM_GET_TEMP	0x10a3
 #define I8K_SMM_GET_DELL_SIG1	0xfea3
 #define I8K_SMM_GET_DELL_SIG2	0xffa3
@@ -275,6 +276,19 @@ 
 	return i8k_smm(&regs) ? : (regs.eax & 0xffff) * i8k_fan_mult;
 }

+
+/*
+ * Read the fan type.
+ */
+static int i8k_get_fan_type(int fan)
+{
+	struct smm_regs regs = { .eax = I8K_SMM_GET_FAN_TYPE, };
+
+	regs.ebx = fan & 0xff;
+	return i8k_smm(&regs) ? : regs.eax & 0xff;
+}
+
+
 /*
  * Set the fan speed (off, low, high). Returns the new fan status.
  */
@@ -870,6 +884,9 @@ 
 	if (err)
 		goto exit_remove_proc;

+	// calling i8k_get_fan_type once
+	printk("testing i8k_get_fan_type (%d)", i8k_get_fan_type(0));
+
 	return 0;

  exit_remove_proc: