Patch "i2c: piix4: Avoid race conditions with IMC" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

i2c: piix4: Avoid race conditions with IMC

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
i2c-piix4-avoid-race-conditions-with-imc.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Ricardo Ribalda <[email protected]>
Date: Wed, 11 Jan 2017 10:11:44 +0100
Subject: i2c: piix4: Avoid race conditions with IMC

From: Ricardo Ribalda Delgado <[email protected]>

commit 701dc207bf551d9fe6defa36e84a911e880398c3 upstream.

On AMD's SB800 and upwards, the SMBus is shared with the Integrated Micro Controller (IMC).

The platform provides a hardware semaphore to avoid race conditions among them. (Check page 288 of the SB800-Series Southbridges Register Reference Guide http://support.amd.com/TechDocs/45482.pdf)

Without this patch, many access to the SMBus end with an invalid transaction or even with the bus stalled.

---
 drivers/i2c/busses/i2c-piix4.c |   22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

@@ -585,10 +585,29 @@ static s32 piix4_access_sb800(struct i2c
 		 u8 command, int size, union i2c_smbus_data *data)
 {
 	struct i2c_piix4_adapdata *adapdata = i2c_get_adapdata(adap);
+	unsigned short piix4_smba = adapdata->smba;
+	int retries = MAX_TIMEOUT;
+	int smbslvcnt;
 	u8 smba_en_lo;
 	u8 port;
 	int retval;
 
+	/* Request the SMBUS semaphore, avoid conflicts with the IMC */
+	smbslvcnt  = inb_p(SMBSLVCNT);
+	do {
+		outb_p(smbslvcnt | 0x10, SMBSLVCNT);
+
+		/* Check the semaphore status */
+		smbslvcnt  = inb_p(SMBSLVCNT);
+		if (smbslvcnt & 0x10)
+			break;
+
+		usleep_range(1000, 2000);
+	} while (--retries);
+	/* SMBus is still owned by the IMC, we give up */
+	if (!retries)
+		return -EBUSY;
+
 	mutex_lock(&piix4_mutex_sb800);
 
 	outb_p(piix4_port_sel_sb800, SB800_PIIX4_SMB_IDX);

@@ -606,6 +625,9 @@ static s32 piix4_access_sb800(struct i2c
 
 	mutex_unlock(&piix4_mutex_sb800);
 
+	/* Release the semaphore */
+	outb_p(smbslvcnt | 0x20, SMBSLVCNT);
+
 	return retval;
 }
 

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/i2c-piix4-avoid-race-conditions-with-imc.patch