i8k: Rework error retries

Instead of returning a previous value if the SMM code returns
an error when trying to read a temperature, retry once.
If that fails again, return -ENODATA. Also return -ENODATA if an
attempt is made to read the GPU temperature but the GPU is
currently turned off.

Drop the I8K_TEMPERATURE_BUG definition and handle the related bug
unconditionally.

Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Tested-by: Pali Rohár <pali.rohar@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 24 insertions, 23 deletions

diff --git a/drivers/char/i8k.c b/drivers/char/i8k.c
index 1854faba8ae6..0e332fcd8fc3 100644
--- a/drivers/char/i8k.c
+++ b/drivers/char/i8k.c
@@ -5,7 +5,7 @@
  *
  * Hwmon integration:
  * Copyright (C) 2011  Jean Delvare <jdelvare@suse.de>
- * Copyright (C) 2013  Guenter Roeck <linux@roeck-us.net>
+ * Copyright (C) 2013, 2014  Guenter Roeck <linux@roeck-us.net>
  *
  * This program is free software; you can redistribute it and/or modify it
  * under the terms of the GNU General Public License as published by the
@@ -20,6 +20,7 @@
 
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 
+#include <linux/delay.h>
 #include <linux/module.h>
 #include <linux/types.h>
 #include <linux/init.h>
@@ -59,8 +60,6 @@
 #define I8K_POWER_AC            0x05
 #define I8K_POWER_BATTERY       0x01
 
-#define I8K_TEMPERATURE_BUG     1
-
 static DEFINE_MUTEX(i8k_mutex);
 static char bios_version[4];
 static struct device *i8k_hwmon_dev;
@@ -300,39 +299,41 @@ static int i8k_get_temp_type(int sensor)
 /*
  * Read the cpu temperature.
  */
-static int i8k_get_temp(int sensor)
+static int _i8k_get_temp(int sensor)
 {
-        struct smm_regs regs = { .eax = I8K_SMM_GET_TEMP, };
-        int rc;
-        int temp;
+        struct smm_regs regs = {
+                .eax = I8K_SMM_GET_TEMP,
+                .ebx = sensor & 0xff,
+        };
 
-#ifdef I8K_TEMPERATURE_BUG
-        static int prev[4] = { I8K_MAX_TEMP+1, I8K_MAX_TEMP+1, I8K_MAX_TEMP+1, I8K_MAX_TEMP+1 };
-#endif
-        regs.ebx = sensor & 0xff;
-        rc = i8k_smm(&regs);
-        if (rc < 0)
-                return rc;
+        return i8k_smm(&regs) ? : regs.eax & 0xff;
+}
 
-        temp = regs.eax & 0xff;
+static int i8k_get_temp(int sensor)
+{
+        int temp = _i8k_get_temp(sensor);
 
-#ifdef I8K_TEMPERATURE_BUG
         /*
          * Sometimes the temperature sensor returns 0x99, which is out of range.
-         * In this case we return (once) the previous cached value. For example:
+         * In this case we retry (once) before returning an error.
          # 1003655137 00000058 00005a4b
          # 1003655138 00000099 00003a80 <--- 0x99 = 153 degrees
          # 1003655139 00000054 00005c52
          */
-        if (temp > I8K_MAX_TEMP) {
-                temp = prev[sensor];
-                prev[sensor] = I8K_MAX_TEMP+1;
-        } else {
-                prev[sensor] = temp;
+        if (temp == 0x99) {
+                msleep(100);
+                temp = _i8k_get_temp(sensor);
         }
+        /*
+         * Return -ENODATA for all invalid temperatures.
+         *
+         * Known instances are the 0x99 value as seen above as well as
+         * 0xc1 (193), which may be returned when trying to read the GPU
+         * temperature if the system supports a GPU and it is currently
+         * turned off.
+         */
         if (temp > I8K_MAX_TEMP)
                 return -ENODATA;
-#endif
 
         return temp;
 }