can: mcp251x: fix resume when device is down

commit 25b401c1 upstream.

If a valid power regulator or a dummy regulator is used (which
happens to be the case when no regulator is specified), restart_work
is queued no matter whether the device was running or not at suspend
time. Since work queues get initialized in the ndo_open callback,
resuming leads to a NULL pointer exception.

Reverse exactly the steps executed at suspend time:
- Enable the power regulator in any case
- Enable the transceiver regulator if the device was running, even in
  case we have a power regulator
- Queue restart_work only in case the device was running

Fixes: bf66f373 ("can: mcp251x: Move to threaded interrupts instead of workqueues.")
Signed-off-by: Stefan Agner <stefan@agner.ch>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
[lizf: Backported to 3.4:
 - adjust filename
 - adjust context]
Signed-off-by: Zefan Li <lizefan@huawei.com>

drivers/net/can/mcp251x.c

@@ -1161,18 +1161,17 @@ static int mcp251x_can_resume(struct spi_device *spi)
 	struct mcp251x_platform_data *pdata = spi->dev.platform_data;
 	struct mcp251x_priv *priv = dev_get_drvdata(&spi->dev);
 
-	if (priv->after_suspend & AFTER_SUSPEND_POWER) {
+	if (priv->after_suspend & AFTER_SUSPEND_POWER)
 		pdata->power_enable(1);
+
+	if (priv->after_suspend & AFTER_SUSPEND_UP) {
+		if (pdata->transceiver_enable)
+			pdata->transceiver_enable(1);
 		queue_work(priv->wq, &priv->restart_work);
 	} else {
-		if (priv->after_suspend & AFTER_SUSPEND_UP) {
-			if (pdata->transceiver_enable)
-				pdata->transceiver_enable(1);
-			queue_work(priv->wq, &priv->restart_work);
-		} else {
-			priv->after_suspend = 0;
-		}
+		priv->after_suspend = 0;
 	}
+
 	priv->force_quit = 0;
 	enable_irq(spi->irq);
 	return 0;