i2c: i801: Ensure that SMBHSTSTS_INUSE_STS is cleared when leaving i801_access

As explained in [0] currently we may leave SMBHSTSTS_INUSE_STS set,
thus potentially breaking ACPI/BIOS usage of the SMBUS device.

Seems patch [0] needs a little bit more of review effort, therefore
I'd suggest to apply a part of it as quick win. Just clearing
SMBHSTSTS_INUSE_STS when leaving i801_access() should fix the
referenced issue and leaves more time for discussing a more
sophisticated locking handling.

[0] https://www.spinics.net/lists/linux-i2c/msg51558.html

Fixes: 01590f3 ("i2c: i801: Instantiate SPD EEPROMs automatically")
Suggested-by: Hector Martin <marcan@marcan.st>
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Reviewed-by: Hector Martin <marcan@marcan.st>
Reviewed-by: Jean Delvare <jdelvare@suse.de>
Tested-by: Jean Delvare <jdelvare@suse.de>
Signed-off-by: Wolfram Sang <wsa@kernel.org>

Author: hkallweit

drivers/i2c/busses/i2c-i801.c

@@ -978,6 +978,9 @@ static s32 i801_access(struct i2c_adapter *adap, u16 addr,
 	}
 
 out:
+	/* Unlock the SMBus device for use by BIOS/ACPI */
+	outb_p(SMBHSTSTS_INUSE_STS, SMBHSTSTS(priv));
+
 	pm_runtime_mark_last_busy(&priv->pci_dev->dev);
 	pm_runtime_put_autosuspend(&priv->pci_dev->dev);
 	mutex_unlock(&priv->acpi_lock);