i2c-i801: Let the user disable selected driver features

Let the user disable selected features normally supported by the
device. This makes it possible to work around possible driver or
hardware bugs if the feature in question doesn't work as intended
for whatever reason.
Signed-off-by: Jean Delvare <khali@linux-fr.org>
Cc: Felix Rubinstein <felixru@gmail.com>

Documentation/i2c/busses/i2c-i801

@@ -27,7 +27,13 @@ Authors:
 Module Parameters
 -----------------
 
-None.
+* disable_features (bit vector)
+Disable selected features normally supported by the device. This makes it
+possible to work around possible driver or hardware bugs if the feature in
+question doesn't work as intended for whatever reason. Bit values:
+  1  disable SMBus PEC
+  2  disable the block buffer
+  8  disable the I2C block read functionality
 
 
 Description

drivers/i2c/busses/i2c-i801.c

@@ -138,6 +138,17 @@ static struct pci_dev *I801_dev;
 #define FEATURE_I2C_BLOCK_READ	(1 << 3)
 static unsigned int i801_features;
 
+static const char *i801_feature_names[] = {
+	"SMBus PEC",
+	"Block buffer",
+	"Block process call",
+	"I2C block read",
+};
+
+static unsigned int disable_features;
+module_param(disable_features, uint, S_IRUGO | S_IWUSR);
+MODULE_PARM_DESC(disable_features, "Disable selected driver features");
+
 /* Make sure the SMBus host is ready to start transmitting.
    Return 0 if it is, -EBUSY if it is not. */
 static int i801_check_pre(void)
@@ -692,7 +703,7 @@ static void __devinit dmi_check_onboard_devices(const struct dmi_header *dm,
 static int __devinit i801_probe(struct pci_dev *dev, const struct pci_device_id *id)
 {
 	unsigned char temp;
-	int err;
+	int err, i;
 #if defined CONFIG_SENSORS_FSCHMD || defined CONFIG_SENSORS_FSCHMD_MODULE
 	const char *vendor;
 #endif
@@ -720,6 +731,14 @@ static int __devinit i801_probe(struct pci_dev *dev, const struct pci_device_id
 		break;
 	}
 
+	/* Disable features on user request */
+	for (i = 0; i < ARRAY_SIZE(i801_feature_names); i++) {
+		if (i801_features & disable_features & (1 << i))
+			dev_notice(&dev->dev, "%s disabled by user\n",
+				   i801_feature_names[i]);
+	}
+	i801_features &= ~disable_features;
+
 	err = pci_enable_device(dev);
 	if (err) {
 		dev_err(&dev->dev, "Failed to enable SMBus PCI device (%d)\n",