[PATCH v2 00/10] i2c: Host Notify / i801 fixes

[PATCH v2 00/10] i2c: Host Notify / i801 fixes

[Benjamin Tissoires]

Hi,

I finally managed to free some time to do a refresh of this series.

I had to add some patches to keep the rev-by from Jean, and also
because it was making more sense to have those remarks in their own
patch.

Cheers,
Benjamin

Benjamin Tissoires (10):
  i2c: i2c-smbus: prevent races on remove when Host Notify is used
  i2c: i801: store and restore the SLVCMD register at load and unload
  i2c: i801: minor formatting issues
  i2c: i801: use BIT() macro for bits definition
  i2c: i801: use the BIT() macro for FEATURES_* also
  i2c: i801: do not report an error if FEATURE_HOST_NOTIFY is not set
  i2c: i2c-smbus: remove double warning message
  i2c: i2c-smbus: fix return value of i2c_handle_smbus_host_notify()
  i2c: i801: warn on i2c_handle_smbus_host_notify() errors
  i2c: i801: remove SMBNTFDDAT reads as they always seem to return 0

 drivers/i2c/busses/i2c-i801.c | 124 ++++++++++++++++++++++++++----------------
 drivers/i2c/i2c-smbus.c       |  25 ++++++++-
 include/linux/i2c-smbus.h     |   1 +
 3 files changed, 100 insertions(+), 50 deletions(-)

-- 
2.5.5

[PATCH v2 01/10] i2c: i2c-smbus: prevent races on remove when Host Notify is used

[Benjamin Tissoires]

struct host_notify contains its own workqueue, so there is a race when
the adapter gets removed:
- the adapter schedules a notification
- the notification is on hold
- the adapter gets removed and all its children too
- the worker fires and access illegal memory

Add an API to actually kill the workqueue and prevent it to access such
illegal memory. I couldn't find a reliable way of automatically calling
this, so it's the responsibility of the adapter driver to clean up after
itself.

Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>

---

changes in v2:
- changed i801_disable_host_notify() parameter
- changed the comments to actually match the behavior
---
 drivers/i2c/busses/i2c-i801.c | 13 +++++++++++++
 drivers/i2c/i2c-smbus.c       | 19 +++++++++++++++++++
 include/linux/i2c-smbus.h     |  1 +
 3 files changed, 33 insertions(+)

diff --git a/drivers/i2c/busses/i2c-i801.c b/drivers/i2c/busses/i2c-i801.c
index 5ef9b73..84eabb1 100644
--- a/drivers/i2c/busses/i2c-i801.c
+++ b/drivers/i2c/busses/i2c-i801.c
@@ -959,6 +959,18 @@ static int i801_enable_host_notify(struct i2c_adapter *adapter)
 	return 0;
 }
 
+static void i801_disable_host_notify(struct i801_priv *priv)
+{
+
+	if (!(priv->features & FEATURE_HOST_NOTIFY))
+		return;
+
+	/* disable Host Notify... */
+	outb_p(0, SMBSLVCMD(priv));
+	/* ...and process the already queued notifications */
+	i2c_cancel_smbus_host_notify(priv->host_notify);
+}
+
 static const struct i2c_algorithm smbus_algorithm = {
 	.smbus_xfer	= i801_access,
 	.functionality	= i801_func,
@@ -1648,6 +1660,7 @@ static void i801_remove(struct pci_dev *dev)
 	pm_runtime_forbid(&dev->dev);
 	pm_runtime_get_noresume(&dev->dev);
 
+	i801_disable_host_notify(priv);
 	i801_del_mux(priv);
 	i2c_del_adapter(&priv->adapter);
 	i801_acpi_remove(priv);
diff --git a/drivers/i2c/i2c-smbus.c b/drivers/i2c/i2c-smbus.c
index b0d2679..35e4f1a 100644
--- a/drivers/i2c/i2c-smbus.c
+++ b/drivers/i2c/i2c-smbus.c
@@ -279,6 +279,8 @@ static void smbus_host_notify_work(struct work_struct *work)
  * Returns a struct smbus_host_notify pointer on success, and NULL on failure.
  * The resulting smbus_host_notify must not be freed afterwards, it is a
  * managed resource already.
+ * To prevent races on remove, the caller needs to stop the embedded worker
+ * by calling i2c_cancel_smbus_host_notify().
  */
 struct smbus_host_notify *i2c_setup_smbus_host_notify(struct i2c_adapter *adap)
 {
@@ -299,6 +301,23 @@ struct smbus_host_notify *i2c_setup_smbus_host_notify(struct i2c_adapter *adap)
 EXPORT_SYMBOL_GPL(i2c_setup_smbus_host_notify);
 
 /**
+ * i2c_cancel_smbus_host_notify - Terminate any active Host Notification.
+ * @host_notify: the host_notify object to terminate
+ *
+ * Process any pending Host Notifcation and prevent new ones to be added.
+ * Must be called to ensure no races between the adaptor being removed and
+ * the Host Notification being processed.
+ */
+void i2c_cancel_smbus_host_notify(struct smbus_host_notify *host_notify)
+{
+	if (!host_notify)
+		return;
+
+	cancel_work_sync(&host_notify->work);
+}
+EXPORT_SYMBOL_GPL(i2c_cancel_smbus_host_notify);
+
+/**
  * i2c_handle_smbus_host_notify - Forward a Host Notify event to the correct
  * I2C client.
  * @host_notify: the struct host_notify attached to the relevant adapter
diff --git a/include/linux/i2c-smbus.h b/include/linux/i2c-smbus.h
index c2e3324..ac02827 100644
--- a/include/linux/i2c-smbus.h
+++ b/include/linux/i2c-smbus.h
@@ -76,5 +76,6 @@ struct smbus_host_notify {
 struct smbus_host_notify *i2c_setup_smbus_host_notify(struct i2c_adapter *adap);
 int i2c_handle_smbus_host_notify(struct smbus_host_notify *host_notify,
 				 unsigned short addr, unsigned int data);
+void i2c_cancel_smbus_host_notify(struct smbus_host_notify *host_notify);
 
 #endif /* _LINUX_I2C_SMBUS_H */
-- 
2.5.5

[PATCH v2 02/10] i2c: i801: store and restore the SLVCMD register at load and unload

[Benjamin Tissoires]

Also do not override any other configuration in this register.

Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>

---

new in v2
---
 drivers/i2c/busses/i2c-i801.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/drivers/i2c/busses/i2c-i801.c b/drivers/i2c/busses/i2c-i801.c
index 84eabb1..179e387 100644
--- a/drivers/i2c/busses/i2c-i801.c
+++ b/drivers/i2c/busses/i2c-i801.c
@@ -240,6 +240,7 @@ struct i801_priv {
 	struct i2c_adapter adapter;
 	unsigned long smba;
 	unsigned char original_hstcfg;
+	unsigned char original_slvcmd;
 	struct pci_dev *pci_dev;
 	unsigned int features;
 
@@ -952,7 +953,12 @@ static int i801_enable_host_notify(struct i2c_adapter *adapter)
 	if (!priv->host_notify)
 		return -ENOMEM;
 
-	outb_p(SMBSLVCMD_HST_NTFY_INTREN, SMBSLVCMD(priv));
+	priv->original_slvcmd = inb_p(SMBSLVCMD(priv));
+
+	if (!(SMBSLVCMD_HST_NTFY_INTREN & priv->original_slvcmd))
+		outb_p(SMBSLVCMD_HST_NTFY_INTREN | priv->original_slvcmd,
+		       SMBSLVCMD(priv));
+
 	/* clear Host Notify bit to allow a new notification */
 	outb_p(SMBSLVSTS_HST_NTFY_STS, SMBSLVSTS(priv));
 
@@ -961,12 +967,11 @@ static int i801_enable_host_notify(struct i2c_adapter *adapter)
 
 static void i801_disable_host_notify(struct i801_priv *priv)
 {
-
 	if (!(priv->features & FEATURE_HOST_NOTIFY))
 		return;
 
 	/* disable Host Notify... */
-	outb_p(0, SMBSLVCMD(priv));
+	outb_p(priv->original_slvcmd, SMBSLVCMD(priv));
 	/* ...and process the already queued notifications */
 	i2c_cancel_smbus_host_notify(priv->host_notify);
 }
-- 
2.5.5

[PATCH v2 03/10] i2c: i801: minor formatting issues

[Benjamin Tissoires]

No functional changes, just typos and remove unused #define.

Reviewed-by: Jean Delvare <jdelvare@suse.de>
Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>

---

no changes in v2
---
 drivers/i2c/busses/i2c-i801.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/drivers/i2c/busses/i2c-i801.c b/drivers/i2c/busses/i2c-i801.c
index 179e387..64da594 100644
--- a/drivers/i2c/busses/i2c-i801.c
+++ b/drivers/i2c/busses/i2c-i801.c
@@ -186,10 +186,10 @@
 #define SMBHSTSTS_INTR		0x02
 #define SMBHSTSTS_HOST_BUSY	0x01
 
-/* Host Notify Status registers bits */
+/* Host Notify Status register bits */
 #define SMBSLVSTS_HST_NTFY_STS	1
 
-/* Host Notify Command registers bits */
+/* Host Notify Command register bits */
 #define SMBSLVCMD_HST_NTFY_INTREN	0x01
 
 #define STATUS_ERROR_FLAGS	(SMBHSTSTS_FAILED | SMBHSTSTS_BUS_ERR | \
@@ -270,8 +270,6 @@ struct i801_priv {
 	struct smbus_host_notify *host_notify;
 };
 
-#define SMBHSTNTFY_SIZE		8
-
 #define FEATURE_SMBUS_PEC	(1 << 0)
 #define FEATURE_BLOCK_BUFFER	(1 << 1)
 #define FEATURE_BLOCK_PROC	(1 << 2)
-- 
2.5.5

[PATCH v2 04/10] i2c: i801: use BIT() macro for bits definition

[Benjamin Tissoires]

i801 mixes hexadecimal and decimal values for defining bits. However,
we have a nice BIT() macro for this exact purpose.

No functional changes, cleanup only.

Reviewed-by: Jean Delvare <jdelvare@suse.de>
Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>

---

no changes in v2
---
 drivers/i2c/busses/i2c-i801.c | 50 +++++++++++++++++++++----------------------
 1 file changed, 25 insertions(+), 25 deletions(-)

diff --git a/drivers/i2c/busses/i2c-i801.c b/drivers/i2c/busses/i2c-i801.c
index 64da594..dc95518 100644
--- a/drivers/i2c/busses/i2c-i801.c
+++ b/drivers/i2c/busses/i2c-i801.c
@@ -136,26 +136,26 @@
 #define SBREG_SMBCTRL		0xc6000c
 
 /* Host status bits for SMBPCISTS */
-#define SMBPCISTS_INTS		0x08
+#define SMBPCISTS_INTS		BIT(3)
 
 /* Control bits for SMBPCICTL */
-#define SMBPCICTL_INTDIS	0x0400
+#define SMBPCICTL_INTDIS	BIT(10)
 
 /* Host configuration bits for SMBHSTCFG */
-#define SMBHSTCFG_HST_EN	1
-#define SMBHSTCFG_SMB_SMI_EN	2
-#define SMBHSTCFG_I2C_EN	4
+#define SMBHSTCFG_HST_EN	BIT(0)
+#define SMBHSTCFG_SMB_SMI_EN	BIT(1)
+#define SMBHSTCFG_I2C_EN	BIT(2)
 
 /* TCO configuration bits for TCOCTL */
-#define TCOCTL_EN		0x0100
+#define TCOCTL_EN		BIT(8)
 
 /* Auxiliary status register bits, ICH4+ only */
-#define SMBAUXSTS_CRCE		1
-#define SMBAUXSTS_STCO		2
+#define SMBAUXSTS_CRCE		BIT(0)
+#define SMBAUXSTS_STCO		BIT(1)
 
 /* Auxiliary control register bits, ICH4+ only */
-#define SMBAUXCTL_CRC		1
-#define SMBAUXCTL_E32B		2
+#define SMBAUXCTL_CRC		BIT(0)
+#define SMBAUXCTL_E32B		BIT(1)
 
 /* Other settings */
 #define MAX_RETRIES		400
@@ -170,27 +170,27 @@
 #define I801_I2C_BLOCK_DATA	0x18	/* ICH5 and later */
 
 /* I801 Host Control register bits */
-#define SMBHSTCNT_INTREN	0x01
-#define SMBHSTCNT_KILL		0x02
-#define SMBHSTCNT_LAST_BYTE	0x20
-#define SMBHSTCNT_START		0x40
-#define SMBHSTCNT_PEC_EN	0x80	/* ICH3 and later */
+#define SMBHSTCNT_INTREN	BIT(0)
+#define SMBHSTCNT_KILL		BIT(1)
+#define SMBHSTCNT_LAST_BYTE	BIT(5)
+#define SMBHSTCNT_START		BIT(6)
+#define SMBHSTCNT_PEC_EN	BIT(7)	/* ICH3 and later */
 
 /* I801 Hosts Status register bits */
-#define SMBHSTSTS_BYTE_DONE	0x80
-#define SMBHSTSTS_INUSE_STS	0x40
-#define SMBHSTSTS_SMBALERT_STS	0x20
-#define SMBHSTSTS_FAILED	0x10
-#define SMBHSTSTS_BUS_ERR	0x08
-#define SMBHSTSTS_DEV_ERR	0x04
-#define SMBHSTSTS_INTR		0x02
-#define SMBHSTSTS_HOST_BUSY	0x01
+#define SMBHSTSTS_BYTE_DONE	BIT(7)
+#define SMBHSTSTS_INUSE_STS	BIT(6)
+#define SMBHSTSTS_SMBALERT_STS	BIT(5)
+#define SMBHSTSTS_FAILED	BIT(4)
+#define SMBHSTSTS_BUS_ERR	BIT(3)
+#define SMBHSTSTS_DEV_ERR	BIT(2)
+#define SMBHSTSTS_INTR		BIT(1)
+#define SMBHSTSTS_HOST_BUSY	BIT(0)
 
 /* Host Notify Status register bits */
-#define SMBSLVSTS_HST_NTFY_STS	1
+#define SMBSLVSTS_HST_NTFY_STS	BIT(0)
 
 /* Host Notify Command register bits */
-#define SMBSLVCMD_HST_NTFY_INTREN	0x01
+#define SMBSLVCMD_HST_NTFY_INTREN	BIT(0)
 
 #define STATUS_ERROR_FLAGS	(SMBHSTSTS_FAILED | SMBHSTSTS_BUS_ERR | \
 				 SMBHSTSTS_DEV_ERR)
-- 
2.5.5

[PATCH v2 05/10] i2c: i801: use the BIT() macro for FEATURES_* also

[Benjamin Tissoires]

no functional changes

Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>

---

new in v2
---
 drivers/i2c/busses/i2c-i801.c | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/drivers/i2c/busses/i2c-i801.c b/drivers/i2c/busses/i2c-i801.c
index dc95518..a5360df8 100644
--- a/drivers/i2c/busses/i2c-i801.c
+++ b/drivers/i2c/busses/i2c-i801.c
@@ -270,15 +270,15 @@ struct i801_priv {
 	struct smbus_host_notify *host_notify;
 };
 
-#define FEATURE_SMBUS_PEC	(1 << 0)
-#define FEATURE_BLOCK_BUFFER	(1 << 1)
-#define FEATURE_BLOCK_PROC	(1 << 2)
-#define FEATURE_I2C_BLOCK_READ	(1 << 3)
-#define FEATURE_IRQ		(1 << 4)
-#define FEATURE_HOST_NOTIFY	(1 << 5)
+#define FEATURE_SMBUS_PEC	BIT(0)
+#define FEATURE_BLOCK_BUFFER	BIT(1)
+#define FEATURE_BLOCK_PROC	BIT(2)
+#define FEATURE_I2C_BLOCK_READ	BIT(3)
+#define FEATURE_IRQ		BIT(4)
+#define FEATURE_HOST_NOTIFY	BIT(5)
 /* Not really a feature, but it's convenient to handle it as such */
-#define FEATURE_IDF		(1 << 15)
-#define FEATURE_TCO		(1 << 16)
+#define FEATURE_IDF		BIT(15)
+#define FEATURE_TCO		BIT(16)
 
 static const char *i801_feature_names[] = {
 	"SMBus PEC",
-- 
2.5.5

[PATCH v2 06/10] i2c: i801: do not report an error if FEATURE_HOST_NOTIFY is not set

[Benjamin Tissoires]

we can skip one test when calling i801_enable_host_notify(). Given
that we call it all the time, it's better to consider the fact that
the adapter doesn't support Host Notify as not an error.

Reviewed-by: Jean Delvare <jdelvare@suse.de>
Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>

---

no changes in v2
---
 drivers/i2c/busses/i2c-i801.c | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/drivers/i2c/busses/i2c-i801.c b/drivers/i2c/busses/i2c-i801.c
index a5360df8..74fb144 100644
--- a/drivers/i2c/busses/i2c-i801.c
+++ b/drivers/i2c/busses/i2c-i801.c
@@ -944,12 +944,13 @@ static int i801_enable_host_notify(struct i2c_adapter *adapter)
 	struct i801_priv *priv = i2c_get_adapdata(adapter);
 
 	if (!(priv->features & FEATURE_HOST_NOTIFY))
-		return -ENOTSUPP;
+		return 0; /* not an error actually */
 
-	if (!priv->host_notify)
+	if (!priv->host_notify) {
 		priv->host_notify = i2c_setup_smbus_host_notify(adapter);
-	if (!priv->host_notify)
-		return -ENOMEM;
+		if (!priv->host_notify)
+			return -ENOMEM;
+	}
 
 	priv->original_slvcmd = inb_p(SMBSLVCMD(priv));
 
@@ -1639,7 +1640,7 @@ static int i801_probe(struct pci_dev *dev, const struct pci_device_id *id)
 	 * is not used if i2c_add_adapter() fails.
 	 */
 	err = i801_enable_host_notify(&priv->adapter);
-	if (err && err != -ENOTSUPP)
+	if (err)
 		dev_warn(&dev->dev, "Unable to enable SMBus Host Notify\n");
 
 	i801_probe_optional_slaves(priv);
@@ -1694,7 +1695,7 @@ static int i801_resume(struct device *dev)
 	int err;
 
 	err = i801_enable_host_notify(&priv->adapter);
-	if (err && err != -ENOTSUPP)
+	if (err)
 		dev_warn(dev, "Unable to enable SMBus Host Notify\n");
 
 	return 0;
-- 
2.5.5

[PATCH v2 07/10] i2c: i2c-smbus: remove double warning message

[Benjamin Tissoires]

i2c_handle_smbus_host_notify() returns an error code when it fails.
If the caller wants to warn when an error is returned, we should not
partially warn in the function itself.

Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>

---

new in v2
---
 drivers/i2c/i2c-smbus.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/drivers/i2c/i2c-smbus.c b/drivers/i2c/i2c-smbus.c
index 35e4f1a..819e5f2 100644
--- a/drivers/i2c/i2c-smbus.c
+++ b/drivers/i2c/i2c-smbus.c
@@ -347,7 +347,6 @@ int i2c_handle_smbus_host_notify(struct smbus_host_notify *host_notify,
 
 	if (host_notify->pending) {
 		spin_unlock_irqrestore(&host_notify->lock, flags);
-		dev_warn(&adapter->dev, "Host Notify already scheduled.\n");
 		return -EBUSY;
 	}
 
-- 
2.5.5

[PATCH v2 08/10] i2c: i2c-smbus: fix return value of i2c_handle_smbus_host_notify()

[Benjamin Tissoires]

schedule_work() returns a boolean (true on success, false if the work
was already queued).
This doesn't match the "negative number on error" return model that the
function exports.

Given that schedule_work() will always return true (we have an internal
.pending check protected by a spinlock), just return false and ignore
the return value of schedule_work().

Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>

---

new in v2
---
 drivers/i2c/i2c-smbus.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/i2c/i2c-smbus.c b/drivers/i2c/i2c-smbus.c
index 819e5f2..f6780de 100644
--- a/drivers/i2c/i2c-smbus.c
+++ b/drivers/i2c/i2c-smbus.c
@@ -357,7 +357,10 @@ int i2c_handle_smbus_host_notify(struct smbus_host_notify *host_notify,
 	host_notify->pending = true;
 	spin_unlock_irqrestore(&host_notify->lock, flags);
 
-	return schedule_work(&host_notify->work);
+	/* schedule_work is called if .pending is false, so it can't fail. */
+	schedule_work(&host_notify->work);
+
+	return 0;
 }
 EXPORT_SYMBOL_GPL(i2c_handle_smbus_host_notify);
 
-- 
2.5.5

[PATCH v2 09/10] i2c: i801: warn on i2c_handle_smbus_host_notify() errors

[Benjamin Tissoires]

There is a chance we get called while Host Notify is not available (yet),
so we need to clear the Host Notify bit in those rare case.

Reviewed-by: Jean Delvare <jdelvare@suse.de>
Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>

---

no changes in v2 (comments addressed in the previous patches)
---
 drivers/i2c/busses/i2c-i801.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/drivers/i2c/busses/i2c-i801.c b/drivers/i2c/busses/i2c-i801.c
index 74fb144..c5ed44c 100644
--- a/drivers/i2c/busses/i2c-i801.c
+++ b/drivers/i2c/busses/i2c-i801.c
@@ -579,12 +579,21 @@ static irqreturn_t i801_host_notify_isr(struct i801_priv *priv)
 {
 	unsigned short addr;
 	unsigned int data;
+	int ret;
+
+	if (unlikely(!priv->host_notify))
+		goto out;
 
 	addr = inb_p(SMBNTFDADD(priv)) >> 1;
 	data = inw_p(SMBNTFDDAT(priv));
 
-	i2c_handle_smbus_host_notify(priv->host_notify, addr, data);
+	ret = i2c_handle_smbus_host_notify(priv->host_notify, addr, data);
+	if (ret < 0)
+		dev_warn(&priv->pci_dev->dev,
+			 "Host Notify handling failed: %d\n", ret);
 
+
+out:
 	/* clear Host Notify bit and return */
 	outb_p(SMBSLVSTS_HST_NTFY_STS, SMBSLVSTS(priv));
 	return IRQ_HANDLED;
-- 
2.5.5

[PATCH v2 10/10] i2c: i801: remove SMBNTFDDAT reads as they always seem to return 0

[Benjamin Tissoires]

On the platform tested, reading SMBNTFDDAT always returns 0 (using 1 read
of a word or 2 of 2 bytes). Given that we are not sure why and that we
don't need to rely on the data parameter in the current users of Host
Notify, remove this part of the code.

If someone wants to re-enable it, just revert this commit and data should
be available.

Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>

---

new in v2
---
 drivers/i2c/busses/i2c-i801.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/i2c/busses/i2c-i801.c b/drivers/i2c/busses/i2c-i801.c
index c5ed44c..2ffebe6 100644
--- a/drivers/i2c/busses/i2c-i801.c
+++ b/drivers/i2c/busses/i2c-i801.c
@@ -117,7 +117,6 @@
 #define SMBSLVSTS(p)	(16 + (p)->smba)	/* ICH3 and later */
 #define SMBSLVCMD(p)	(17 + (p)->smba)	/* ICH3 and later */
 #define SMBNTFDADD(p)	(20 + (p)->smba)	/* ICH3 and later */
-#define SMBNTFDDAT(p)	(22 + (p)->smba)	/* ICH3 and later */
 
 /* PCI Address Constants */
 #define SMBBAR		4
@@ -578,16 +577,19 @@ static void i801_isr_byte_done(struct i801_priv *priv)
 static irqreturn_t i801_host_notify_isr(struct i801_priv *priv)
 {
 	unsigned short addr;
-	unsigned int data;
 	int ret;
 
 	if (unlikely(!priv->host_notify))
 		goto out;
 
 	addr = inb_p(SMBNTFDADD(priv)) >> 1;
-	data = inw_p(SMBNTFDDAT(priv));
 
-	ret = i2c_handle_smbus_host_notify(priv->host_notify, addr, data);
+	/*
+	 * With the tested platforms, reading SMBNTFDDAT (22 + (p)->smba)
+	 * always returns 0 and is safe to read.
+	 * We just use 0 given we have no use of the data right now.
+	 */
+	ret = i2c_handle_smbus_host_notify(priv->host_notify, addr, 0);
 	if (ret < 0)
 		dev_warn(&priv->pci_dev->dev,
 			 "Host Notify handling failed: %d\n", ret);
-- 
2.5.5