i2c: designware: Add i2c bus locking support

Adds support for acquiring and releasing a hardware bus lock in the i2c
designware core transfer function. This is needed for i2c bus controllers
that are shared with but not controlled by the kernel.

Signed-off-by: David E. Box <[e-mail]>
Reviewed-by: Mika Westerberg <[e-mail]>
Signed-off-by: Wolfram Sang <[e-mail]>

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

···
 	u32 hcnt, lcnt;
 	u32 reg;
 	u32 sda_falling_time, scl_falling_time;
+	int ret;
+
+	if (dev->acquire_lock) {
+		ret = dev->acquire_lock(dev);
+		if (ret) {
+			dev_err(dev->dev, "couldn't acquire bus ownership\n");
+			return ret;
+		}
+	}
 
 	input_clock_khz = dev->get_clk_rate_khz(dev);
 
···
 	} else if (reg != DW_IC_COMP_TYPE_VALUE) {
 		dev_err(dev->dev, "Unknown Synopsys component type: "
 			"0x%08x\n", reg);
+		if (dev->release_lock)
+			dev->release_lock(dev);
 		return -ENODEV;
 	}
 
···
 
 	/* configure the i2c master */
 	dw_writel(dev, dev->master_cfg , DW_IC_CON);
+
+	if (dev->release_lock)
+		dev->release_lock(dev);
 	return 0;
 }
 EXPORT_SYMBOL_GPL(i2c_dw_init);
···
 	dev->abort_source = 0;
 	dev->rx_outstanding = 0;
 
+	if (dev->acquire_lock) {
+		ret = dev->acquire_lock(dev);
+		if (ret) {
+			dev_err(dev->dev, "couldn't acquire bus ownership\n");
+			goto done_nolock;
+		}
+	}
+
 	ret = i2c_dw_wait_bus_not_busy(dev);
 	if (ret < 0)
 		goto done;
···
 	ret = -EIO;
 
 done:
+	if (dev->release_lock)
+		dev->release_lock(dev);
+
+done_nolock:
 	pm_runtime_mark_last_busy(dev->dev);
 	pm_runtime_put_autosuspend(dev->dev);
 	mutex_unlock(&dev->lock);

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

···
  * @ss_lcnt: standard speed LCNT value
  * @fs_hcnt: fast speed HCNT value
  * @fs_lcnt: fast speed LCNT value
+ * @acquire_lock: function to acquire a hardware lock on the bus
+ * @release_lock: function to release a hardware lock on the bus
+ * @pm_runtime_disabled: true if pm runtime is disabled
  *
  * HCNT and LCNT parameters can be used if the platform knows more accurate
  * values than the one computed based only on the input clock frequency.
···
 	u16			ss_lcnt;
 	u16			fs_hcnt;
 	u16			fs_lcnt;
+	int			(*acquire_lock)(struct dw_i2c_dev *dev);
+	void			(*release_lock)(struct dw_i2c_dev *dev);
+	bool			pm_runtime_disabled;
 };
 
 #define ACCESS_SWAP		0x00000001