Patch "hwmon: (dell-smm) Cache fan_type() calls and change fan detection" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

hwmon: (dell-smm) Cache fan_type() calls and change fan detection

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
hwmon-dell-smm-cache-fan_type-calls-and-change-fan-detection.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: =?UTF-8?q?Pali=20Roh=C3=A1r?= <[email protected]>
Date: Sat, 18 Jun 2016 00:54:47 +0200
Subject: hwmon: (dell-smm) Cache fan_type() calls and change fan detection
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From: Pali Rohár <[email protected]>

commit 5ce91714b0d8c0a3ff9b858966721f508351cf4c upstream.

On more Dell machines (e.g. Dell Precision M3800) fan_type() call is too expensive (CPU is too long in SMM mode) and cause kernel to hang. This is bug in Dell SMM or BIOS.

This patch caches type for each fan (as it should not change) and changes the way how fan presense is detected. First it try function fan_status() as was before commit f989e55452c7 ("i8k: Add support for fan labels"). And if that fails fallback to fan_type(). *_status() functions can fail in case fan is not currently accessible (e.g. present on GPU which is currently turned off).

---
 drivers/hwmon/dell-smm-hwmon.c |   25 ++++++++++++++++++++-----
 1 file changed, 20 insertions(+), 5 deletions(-)

@@ -237,7 +237,7 @@ static int i8k_get_fan_speed(int fan)
 /*
  * Read the fan type.
  */
-static int i8k_get_fan_type(int fan)
+static int _i8k_get_fan_type(int fan)
 {
 	struct smm_regs regs = { .eax = I8K_SMM_GET_FAN_TYPE, };
 

@@ -248,6 +248,17 @@ static int i8k_get_fan_type(int fan)
 	return i8k_smm(&regs) ? : regs.eax & 0xff;
 }
 
+static int i8k_get_fan_type(int fan)
+{
+	/* I8K_SMM_GET_FAN_TYPE SMM call is expensive, so cache values */
+	static int types[2] = { INT_MIN, INT_MIN };
+
+	if (types[fan] == INT_MIN)
+		types[fan] = _i8k_get_fan_type(fan);
+
+	return types[fan];
+}
+
 /*
  * Read the fan nominal rpm for specific fan speed.
  */

@@ -777,13 +788,17 @@ static int __init i8k_init_hwmon(void)
 	if (err >= 0)
 		i8k_hwmon_flags |= I8K_HWMON_HAVE_TEMP4;
 
-	/* First fan attributes, if fan type is OK */
-	err = i8k_get_fan_type(0);
+	/* First fan attributes, if fan status or type is OK */
+	err = i8k_get_fan_status(0);
+	if (err < 0)
+		err = i8k_get_fan_type(0);
 	if (err >= 0)
 		i8k_hwmon_flags |= I8K_HWMON_HAVE_FAN1;
 
-	/* Second fan attributes, if fan type is OK */
-	err = i8k_get_fan_type(1);
+	/* Second fan attributes, if fan status or type is OK */
+	err = i8k_get_fan_status(1);
+	if (err < 0)
+		err = i8k_get_fan_type(1);
 	if (err >= 0)
 		i8k_hwmon_flags |= I8K_HWMON_HAVE_FAN2;
 

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/hwmon-dell-smm-disallow-fan_type-calls-on-broken-machines.patch queue-4.4/hwmon-dell-smm-restrict-fan-control-and-serial-number-to-cap_sys_admin-by-default.patch queue-4.4/hwmon-dell-smm-cache-fan_type-calls-and-change-fan-detection.patch