1 files changed, 39 insertions, 1 deletions

diff --git a/drivers/hwmon/dell-smm-hwmon.c b/drivers/hwmon/dell-smm-hwmon.c
index aef4f8317ae2..3f8b4e482b64 100644
--- a/drivers/hwmon/dell-smm-hwmon.c
+++ b/drivers/hwmon/dell-smm-hwmon.c
@@ -76,6 +76,7 @@ static uint i8k_fan_mult = I8K_FAN_MULT;
 static uint i8k_pwm_mult;
 static uint i8k_fan_max = I8K_FAN_HIGH;
 static bool disallow_fan_type_call;
+static bool disallow_fan_support;
 
 #define I8K_HWMON_HAVE_TEMP1    (1 << 0)
 #define I8K_HWMON_HAVE_TEMP2    (1 << 1)
@@ -242,6 +243,9 @@ static int i8k_get_fan_status(int fan)
 {
         struct smm_regs regs = { .eax = I8K_SMM_GET_FAN, };
 
+        if (disallow_fan_support)
+                return -EINVAL;
+
         regs.ebx = fan & 0xff;
         return i8k_smm(&regs) ? : regs.eax & 0xff;
 }
@@ -253,6 +257,9 @@ static int i8k_get_fan_speed(int fan)
 {
         struct smm_regs regs = { .eax = I8K_SMM_GET_SPEED, };
 
+        if (disallow_fan_support)
+                return -EINVAL;
+
         regs.ebx = fan & 0xff;
         return i8k_smm(&regs) ? : (regs.eax & 0xffff) * i8k_fan_mult;
 }
@@ -264,7 +271,7 @@ static int _i8k_get_fan_type(int fan)
 {
         struct smm_regs regs = { .eax = I8K_SMM_GET_FAN_TYPE, };
 
-        if (disallow_fan_type_call)
+        if (disallow_fan_support || disallow_fan_type_call)
                 return -EINVAL;
 
         regs.ebx = fan & 0xff;
@@ -289,6 +296,9 @@ static int i8k_get_fan_nominal_speed(int fan, int speed)
 {
         struct smm_regs regs = { .eax = I8K_SMM_GET_NOM_SPEED, };
 
+        if (disallow_fan_support)
+                return -EINVAL;
+
         regs.ebx = (fan & 0xff) | (speed << 8);
         return i8k_smm(&regs) ? : (regs.eax & 0xffff) * i8k_fan_mult;
 }
@@ -300,6 +310,9 @@ static int i8k_set_fan(int fan, int speed)
 {
         struct smm_regs regs = { .eax = I8K_SMM_SET_FAN, };
 
+        if (disallow_fan_support)
+                return -EINVAL;
+
         speed = (speed < 0) ? 0 : ((speed > i8k_fan_max) ? i8k_fan_max : speed);
         regs.ebx = (fan & 0xff) | (speed << 8);
 
@@ -772,6 +785,8 @@ static struct attribute *i8k_attrs[] = {
 static umode_t i8k_is_visible(struct kobject *kobj, struct attribute *attr,
                               int index)
 {
+        if (disallow_fan_support && index >= 8)
+                return 0;
         if (disallow_fan_type_call &&
             (index == 9 || index == 12 || index == 15))
                 return 0;
@@ -1039,6 +1054,23 @@ static const struct dmi_system_id i8k_blacklist_fan_type_dmi_table[] __initconst
 };
 
 /*
+ * On some machines all fan related SMM functions implemented by Dell BIOS
+ * firmware freeze kernel for about 500ms. Until Dell fixes these problems fan
+ * support for affected blacklisted Dell machines stay disabled.
+ * See bug: https://bugzilla.kernel.org/show_bug.cgi?id=195751
+ */
+static struct dmi_system_id i8k_blacklist_fan_support_dmi_table[] __initdata = {
+        {
+                .ident = "Dell Inspiron 7720",
+                .matches = {
+                        DMI_MATCH(DMI_SYS_VENDOR, "Dell Inc."),
+                        DMI_EXACT_MATCH(DMI_PRODUCT_NAME, "Inspiron 7720"),
+                },
+        },
+        { }
+};
+
+/*
  * Probe for the presence of a supported laptop.
  */
 static int __init i8k_probe(void)
@@ -1060,6 +1092,12 @@ static int __init i8k_probe(void)
                         i8k_get_dmi_data(DMI_BIOS_VERSION));
         }
 
+        if (dmi_check_system(i8k_blacklist_fan_support_dmi_table)) {
+                pr_warn("broken Dell BIOS detected, disallow fan support\n");
+                if (!force)
+                        disallow_fan_support = true;
+        }
+
         if (dmi_check_system(i8k_blacklist_fan_type_dmi_table)) {
                 pr_warn("broken Dell BIOS detected, disallow fan type call\n");
                 if (!force)