drm/fb-helper: Remove drm_fb_helper_unprepare() from drm_fb_helper_fini()

Move drm_fb_helper_unprepare() from drm_fb_helper_fini() into the
calling fbdev implementation. Avoids a possible stale mutex with
generic fbdev code.

As indicated by its name, drm_fb_helper_prepare() prepares struct
drm_fb_helper before setting up the fbdev support with a call to
drm_fb_helper_init(). In legacy fbdev emulation, this happens next
to each other. If successful, drm_fb_helper_fini() later tear down
the fbdev device and also unprepare via drm_fb_helper_unprepare().

Generic fbdev emulation prepares struct drm_fb_helper immediately
after allocating the instance. It only calls drm_fb_helper_init()
as part of processing a hotplug event. If the hotplug-handling fails,
it runs drm_fb_helper_fini(). This unprepares the fb-helper instance
and the next hotplug event runs on stale data.

Solve this by moving drm_fb_helper_unprepare() from drm_fb_helper_fini()
into the fbdev implementations. Call it right before freeing the
fb-helper instance.

Fixes: 643231b28380 ("drm/fbdev-generic: Minimize hotplug error handling")
Cc: Thomas Zimmermann <[email protected]>
Cc: Javier Martinez Canillas <[email protected]>
Cc: Maarten Lankhorst <[email protected]>
Cc: Maxime Ripard <[email protected]>
Cc: David Airlie <[email protected]>
Cc: Daniel Vetter <[email protected]>
Cc: [email protected]
Signed-off-by: Thomas Zimmermann <[email protected]>
Reviewed-by: Daniel Vetter <[email protected]>
Reviewed-by: Javier Martinez Canillas <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]

1 files changed, 2 insertions, 0 deletions

diff --git a/drivers/gpu/drm/omapdrm/omap_fbdev.c b/drivers/gpu/drm/omapdrm/omap_fbdev.c
index fc5f52d567c6..84429728347f 100644
--- a/drivers/gpu/drm/omapdrm/omap_fbdev.c
+++ b/drivers/gpu/drm/omapdrm/omap_fbdev.c
@@ -256,6 +256,7 @@ void omap_fbdev_init(struct drm_device *dev)
 fini:
 	drm_fb_helper_fini(helper);
 fail:
+	drm_fb_helper_unprepare(helper);
 	kfree(fbdev);
 
 	dev_warn(dev->dev, "omap_fbdev_init failed\n");
@@ -286,6 +287,7 @@ void omap_fbdev_fini(struct drm_device *dev)
 	if (fbdev->fb)
 		drm_framebuffer_remove(fbdev->fb);
 
+	drm_fb_helper_unprepare(helper);
 	kfree(fbdev);
 
 	priv->fbdev = NULL;