drm/msm: Get irq number within kms driver itself

The driver gets the irq number using platform_get_irq on the main kms
platform device. This works fine since both MDP4 and MDP5 currently
have a flat device hierarchy. The platform device tied with the
drm_device points to the MDP DT node in both cases.

This won't work when MDP5 supports a tree-like hierarchy. In this
case, the platform device tied to the top level drm_device is the
MDSS DT node, and the irq we need for KMS is the one generated by
MDP5, not MDSS.

Get the irq number from the MDP4/5 kms driver itself. Each driver
can later provide the irq number based on what device hierarchy it
uses.

While we're at it, call drm_irq_install only when we have a valid KMS
driver.

Signed-off-by: Archit Taneja <architt@codeaurora.org>
Signed-off-by: Rob Clark <robdclark@gmail.com>
diff --git a/drivers/gpu/drm/msm/msm_drv.c b/drivers/gpu/drm/msm/msm_drv.c
index 476eafe..092926b 100644
--- a/drivers/gpu/drm/msm/msm_drv.c
+++ b/drivers/gpu/drm/msm/msm_drv.c
@@ -417,12 +417,14 @@
 		goto fail;
 	}
 
-	pm_runtime_get_sync(dev);
-	ret = drm_irq_install(ddev, platform_get_irq(pdev, 0));
-	pm_runtime_put_sync(dev);
-	if (ret < 0) {
-		dev_err(dev, "failed to install IRQ handler\n");
-		goto fail;
+	if (kms) {
+		pm_runtime_get_sync(dev);
+		ret = drm_irq_install(ddev, kms->irq);
+		pm_runtime_put_sync(dev);
+		if (ret < 0) {
+			dev_err(dev, "failed to install IRQ handler\n");
+			goto fail;
+		}
 	}
 
 	ret = drm_dev_register(ddev, 0);