i2c: designware: Disable SMBus interrupts to prevent storms from mis-configured firmware

When probing the I2C master, disable SMBus interrupts to prevent
storms caused by broken firmware mis-configuring IC_SMBUS=1; the
handler never services them and a mis-configured SMBUS Master
extend-clock timeout or SMBUS Slave extend-clock timeout can
flood the CPU.

Signed-off-by: Jinhui Guo <guojinhui.liam@bytedance.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Andi Shyti <andi.shyti@kernel.org>
Link: https://lore.kernel.org/r/20251021075714.3712-2-guojinhui.liam@bytedance.com

Author: guojinhui-liam

drivers/i2c/busses/i2c-designware-core.h

@@ -78,6 +78,7 @@
 #define DW_IC_TX_ABRT_SOURCE			0x80
 #define DW_IC_ENABLE_STATUS			0x9c
 #define DW_IC_CLR_RESTART_DET			0xa8
+#define DW_IC_SMBUS_INTR_MASK			0xcc
 #define DW_IC_COMP_PARAM_1			0xf4
 #define DW_IC_COMP_VERSION			0xf8
 #define DW_IC_SDA_HOLD_MIN_VERS			0x3131312A /* "111*" == v1.11* */

drivers/i2c/busses/i2c-designware-master.c

@@ -220,6 +220,13 @@ static int i2c_dw_init_master(struct dw_i2c_dev *dev)
 	/* Disable the adapter */
 	__i2c_dw_disable(dev);
 
+	/*
+	 * Mask SMBus interrupts to block storms from broken
+	 * firmware that leaves IC_SMBUS=1; the handler never
+	 * services them.
+	 */
+	regmap_write(dev->map, DW_IC_SMBUS_INTR_MASK, 0);
+
 	/* Write standard speed timing parameters */
 	regmap_write(dev->map, DW_IC_SS_SCL_HCNT, dev->ss_hcnt);
 	regmap_write(dev->map, DW_IC_SS_SCL_LCNT, dev->ss_lcnt);