staging: imx/drm: request irq only after adding the crtc

If the bootloader already enabled the display, the interrupt handler
will be called as soon as it is registered. If the CRTC is not already
added at this time, the call to imx_drm_handle_vblank will result in
a NULL pointer dereference.

The patch fixes a kernel panic [1], which has been on linux-next since
Jan 8 [2].

[1] http://thread.gmane.org/gmane.linux.ports.arm.kernel/218858
[2] http://thread.gmane.org/gmane.linux.ports.arm.kernel/208192

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Tested-by: Shawn Guo <shawn.guo@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/imx-drm/ipuv3-crtc.c

@@ -483,17 +483,6 @@ static int ipu_get_resources(struct ipu_crtc *ipu_crtc,
 		goto err_out;
 	}
 
-	ipu_crtc->irq = ipu_idmac_channel_irq(ipu, ipu_crtc->ipu_ch,
-			IPU_IRQ_EOF);
-	ret = devm_request_irq(ipu_crtc->dev, ipu_crtc->irq, ipu_irq_handler, 0,
-			"imx_drm", ipu_crtc);
-	if (ret < 0) {
-		dev_err(ipu_crtc->dev, "irq request failed with %d.\n", ret);
-		goto err_out;
-	}
-
-	disable_irq(ipu_crtc->irq);
-
 	return 0;
 err_out:
 	ipu_put_resources(ipu_crtc);
@@ -504,6 +493,7 @@ static int ipu_get_resources(struct ipu_crtc *ipu_crtc,
 static int ipu_crtc_init(struct ipu_crtc *ipu_crtc,
 		struct ipu_client_platformdata *pdata)
 {
+	struct ipu_soc *ipu = dev_get_drvdata(ipu_crtc->dev->parent);
 	int ret;
 
 	ret = ipu_get_resources(ipu_crtc, pdata);
@@ -522,6 +512,17 @@ static int ipu_crtc_init(struct ipu_crtc *ipu_crtc,
 		goto err_put_resources;
 	}
 
+	ipu_crtc->irq = ipu_idmac_channel_irq(ipu, ipu_crtc->ipu_ch,
+			IPU_IRQ_EOF);
+	ret = devm_request_irq(ipu_crtc->dev, ipu_crtc->irq, ipu_irq_handler, 0,
+			"imx_drm", ipu_crtc);
+	if (ret < 0) {
+		dev_err(ipu_crtc->dev, "irq request failed with %d.\n", ret);
+		goto err_put_resources;
+	}
+
+	disable_irq(ipu_crtc->irq);
+
 	return 0;
 
 err_put_resources: