[PATCH] i2c-piix4: Fix SB800 locking

[Jean Delvare <jdelvare@suse.de>]

We need a single mutex for all 4 shared SMBus ports on the SB800. A
per-port mutex doesn't protect us from concurrent access.

In theory the mutex should be per PCI device, however in practice we
know that there's only ever a single instance of the device in a given
system so we can use a global.

Also take the mutex during initialization, as first port may be already
in use when second port is initialized.

Signed-off-by: Jean Delvare <jdelvare@suse.de>
Cc: Christian Fetzer <fetzer.ch@gmail.com>
Cc: Mika Westerberg <mika.westerberg@linux.intel.com>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Wolfram Sang <wsa@the-dreams.de>
---
 drivers/i2c/busses/i2c-piix4.c |   22 ++++++----------------
 1 file changed, 6 insertions(+), 16 deletions(-)

--- linux-4.5-rc0.orig/drivers/i2c/busses/i2c-piix4.c	2016-01-22 13:51:27.500458587 +0100
+++ linux-4.5-rc0/drivers/i2c/busses/i2c-piix4.c	2016-01-22 13:56:13.210960522 +0100
@@ -137,6 +137,7 @@ static const struct dmi_system_id piix4_
 };
 
 /* SB800 globals */
+DEFINE_MUTEX(piix4_mutex_sb800);
 static const char *piix4_main_port_names_sb800[PIIX4_MAX_ADAPTERS] = {
 	"SDA0", "SDA2", "SDA3", "SDA4"
 };
@@ -148,7 +149,6 @@ struct i2c_piix4_adapdata {
 	/* SB800 */
 	bool sb800_main;
 	unsigned short port;
-	struct mutex *mutex;
 };
 
 static int piix4_setup(struct pci_dev *PIIX4_dev,
@@ -275,10 +275,12 @@ static int piix4_setup_sb800(struct pci_
 	else
 		smb_en = (aux) ? 0x28 : 0x2c;
 
+	mutex_lock(&piix4_mutex_sb800);
 	outb_p(smb_en, SB800_PIIX4_SMB_IDX);
 	smba_en_lo = inb_p(SB800_PIIX4_SMB_IDX + 1);
 	outb_p(smb_en + 1, SB800_PIIX4_SMB_IDX);
 	smba_en_hi = inb_p(SB800_PIIX4_SMB_IDX + 1);
+	mutex_unlock(&piix4_mutex_sb800);
 
 	if (!smb_en) {
 		smb_en_status = smba_en_lo & 0x10;
@@ -559,7 +561,7 @@ static s32 piix4_access_sb800(struct i2c
 	u8 port;
 	int retval;
 
-	mutex_lock(adapdata->mutex);
+	mutex_lock(&piix4_mutex_sb800);
 
 	outb_p(SB800_PIIX4_PORT_IDX, SB800_PIIX4_SMB_IDX);
 	smba_en_lo = inb_p(SB800_PIIX4_SMB_IDX + 1);
@@ -574,7 +576,7 @@ static s32 piix4_access_sb800(struct i2c
 
 	outb_p(smba_en_lo, SB800_PIIX4_SMB_IDX + 1);
 
-	mutex_unlock(adapdata->mutex);
+	mutex_unlock(&piix4_mutex_sb800);
 
 	return retval;
 }
@@ -673,17 +675,10 @@ static int piix4_add_adapter(struct pci_
 
 static int piix4_add_adapters_sb800(struct pci_dev *dev, unsigned short smba)
 {
-	struct mutex *mutex;
 	struct i2c_piix4_adapdata *adapdata;
 	int port;
 	int retval;
 
-	mutex = kzalloc(sizeof(*mutex), GFP_KERNEL);
-	if (mutex == NULL)
-		return -ENOMEM;
-
-	mutex_init(mutex);
-
 	for (port = 0; port < PIIX4_MAX_ADAPTERS; port++) {
 		retval = piix4_add_adapter(dev, smba,
 					   piix4_main_port_names_sb800[port],
@@ -696,7 +691,6 @@ static int piix4_add_adapters_sb800(stru
 		adapdata = i2c_get_adapdata(piix4_main_adapters[port]);
 		adapdata->sb800_main = true;
 		adapdata->port = port;
-		adapdata->mutex = mutex;
 	}
 
 	return retval;
@@ -714,8 +708,6 @@ error:
 		}
 	}
 
-	kfree(mutex);
-
 	return retval;
 }
 
@@ -798,10 +790,8 @@ static void piix4_adap_remove(struct i2c
 		i2c_del_adapter(adap);
 		if (adapdata->port == 0) {
 			release_region(adapdata->smba, SMBIOSIZE);
-			if (adapdata->sb800_main) {
-				kfree(adapdata->mutex);
+			if (adapdata->sb800_main)
 				release_region(SB800_PIIX4_SMB_IDX, 2);
-			}
 		}
 		kfree(adapdata);
 		kfree(adap);


-- 
Jean Delvare
SUSE L3 Support