platform/x86: mlx-platform: Add deffered bus functionality

mlx-platform activates i2c-mux-reg, which creates buses needed by
mlxreg-hotplug. If the mlxreg-hotplug probe runs before the i2c-mux-reg
probe completes, it may attempt to connect a device to an adapter number
that has not been created yet, and fail.

Make mlx-platform driver record the highest bus number in mlxreg-hotplug
platform data and defer mlxreg-hotplug probe until all the buses are
created.

Signed-off-by: Vadim Pasternak <vadimp@mellanox.com>
[dvhart: rewrite commit message more concisely]
Signed-off-by: Darren Hart (VMware) <dvhart@infradead.org>

drivers/platform/mellanox/mlxreg-hotplug.c

@@ -550,6 +550,7 @@ static int mlxreg_hotplug_probe(struct platform_device *pdev)
 {
 	struct mlxreg_core_hotplug_platform_data *pdata;
 	struct mlxreg_hotplug_priv_data *priv;
+	struct i2c_adapter *deferred_adap;
 	int err;
 
 	pdata = dev_get_platdata(&pdev->dev);
@@ -558,6 +559,12 @@ static int mlxreg_hotplug_probe(struct platform_device *pdev)
 		return -EINVAL;
 	}
 
+	/* Defer probing if the necessary adapter is not configured yet. */
+	deferred_adap = i2c_get_adapter(pdata->deferred_nr);
+	if (!deferred_adap)
+		return -EPROBE_DEFER;
+	i2c_put_adapter(deferred_adap);
+
 	priv = devm_kzalloc(&pdev->dev, sizeof(*priv), GFP_KERNEL);
 	if (!priv)
 		return -ENOMEM;