[PATCH] drm/msm: Make .remove and .shutdown HW shutdown consistent

[Javier Martinez Canillas <javierm@redhat.com>]

Drivers' .remove and .shutdown callbacks are executed on different code
paths. The former is called when a device is removed from the bus, while
the latter is called at system shutdown time to quiesce the device.

This means that some overlap exists between the two, because both have to
take care of properly shutting down the hardware. But currently the logic
used in these two callbacks isn't consistent in msm drivers, which could
lead to kernel oops.

For example, on .remove the component is deleted and its .unbind callback
leads to the hardware being shutdown but only if the DRM device has been
marked as registered.

That check doesn't exist in the .shutdown logic and this can lead to the
driver calling drm_atomic_helper_shutdown() for a DRM device that hasn't
been properly initialized.

A situation when this can happen is when a driver for an expected device
fails to probe, since the .bind callback will never be executed.

This bug was attempted to be fixed in commit 623f279c7781 ("drm/msm: fix
shutdown hook in case GPU components failed to bind"), but unfortunately
it still happens in some cases.

Rather than trying to keep fixing in both places, let's unify in a single
helper function that could be used for the two callbacks.

Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
---

 drivers/gpu/drm/msm/msm_drv.c | 31 +++++++++++++++++--------------
 1 file changed, 17 insertions(+), 14 deletions(-)

diff --git a/drivers/gpu/drm/msm/msm_drv.c b/drivers/gpu/drm/msm/msm_drv.c
index 1ed4cd09dbf8..669891bd6f09 100644
--- a/drivers/gpu/drm/msm/msm_drv.c
+++ b/drivers/gpu/drm/msm/msm_drv.c
@@ -190,14 +190,8 @@ static int vblank_ctrl_queue_work(struct msm_drm_private *priv,
 	return 0;
 }
 
-static int msm_drm_uninit(struct device *dev)
+static void msm_shutdown_hw(struct drm_device *dev)
 {
-	struct platform_device *pdev = to_platform_device(dev);
-	struct msm_drm_private *priv = platform_get_drvdata(pdev);
-	struct drm_device *ddev = priv->dev;
-	struct msm_kms *kms = priv->kms;
-	int i;
-
 	/*
 	 * Shutdown the hw if we're far enough along where things might be on.
 	 * If we run this too early, we'll end up panicking in any variety of
@@ -205,10 +199,21 @@ static int msm_drm_uninit(struct device *dev)
 	 * msm_drm_init, drm_dev->registered is used as an indicator that the
 	 * shutdown will be successful.
 	 */
-	if (ddev->registered) {
+	if (dev->registered)
+		drm_atomic_helper_shutdown(dev);
+}
+
+static int msm_drm_uninit(struct device *dev)
+{
+	struct platform_device *pdev = to_platform_device(dev);
+	struct msm_drm_private *priv = platform_get_drvdata(pdev);
+	struct drm_device *ddev = priv->dev;
+	struct msm_kms *kms = priv->kms;
+	int i;
+
+	if (ddev->registered)
 		drm_dev_unregister(ddev);
-		drm_atomic_helper_shutdown(ddev);
-	}
+	msm_shutdown_hw(ddev);
 
 	/* We must cancel and cleanup any pending vblank enable/disable
 	 * work before msm_irq_uninstall() to avoid work re-enabling an
@@ -1242,10 +1247,8 @@ void msm_drv_shutdown(struct platform_device *pdev)
 	struct msm_drm_private *priv = platform_get_drvdata(pdev);
 	struct drm_device *drm = priv ? priv->dev : NULL;
 
-	if (!priv || !priv->kms)
-		return;
-
-	drm_atomic_helper_shutdown(drm);
+	if (drm)
+		msm_shutdown_hw(drm);
 }
 
 static struct platform_driver msm_platform_driver = {
-- 
2.37.1