i2c: piix4: Avoid race conditions with IMC

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.

Reported-by: Alexandre Desnoyers <alex@qtec.com>
Signed-off-by: Ricardo Ribalda Delgado <ricardo.ribalda@gmail.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>:
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>

diff --git a/drivers/i2c/busses/i2c-piix4.c b/drivers/i2c/busses/i2c-piix4.c
index c2268cdf38e82348ae883c99d1f140a7fc2d0ecc..e34d82e79b988a781010cad1e0f283617dfb8471 100644 (file)
--- a/drivers/i2c/busses/i2c-piix4.c
+++ b/drivers/i2c/busses/i2c-piix4.c
@@ -585,10 +585,29 @@ static s32 piix4_access_sb800(struct i2c_adapter *adap, u16 addr,
                 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_adapter *adap, u16 addr,
 
        mutex_unlock(&piix4_mutex_sb800);
 
+       /* Release the semaphore */
+       outb_p(smbslvcnt | 0x20, SMBSLVCNT);
+
        return retval;
 }