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: 643231b2 ("drm/fbdev-generic: Minimize hotplug error handling")
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Javier Martinez Canillas <javierm@redhat.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Maxime Ripard <mripard@kernel.org>
Cc: David Airlie <airlied@gmail.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230216140620.17699-1-tzimmermann@suse.de

drivers/gpu/drm/armada/armada_fbdev.c

@@ -147,6 +147,7 @@ int armada_fbdev_init(struct drm_device *dev)
  err_fb_setup:
 	drm_fb_helper_fini(fbh);
  err_fb_helper:
+	drm_fb_helper_unprepare(fbh);
 	priv->fbdev = NULL;
 	return ret;
 }
@@ -164,6 +165,8 @@ void armada_fbdev_fini(struct drm_device *dev)
 		if (fbh->fb)
 			fbh->fb->funcs->destroy(fbh->fb);
 
+		drm_fb_helper_unprepare(fbh);
+
 		priv->fbdev = NULL;
 	}
 }

drivers/gpu/drm/drm_fb_helper.c

@@ -590,8 +590,6 @@ void drm_fb_helper_fini(struct drm_fb_helper *fb_helper)
 	}
 	mutex_unlock(&kernel_fb_helper_lock);
 
-	drm_fb_helper_unprepare(fb_helper);
-
 	if (!fb_helper->client.funcs)
 		drm_client_release(&fb_helper->client);
 }

drivers/gpu/drm/drm_fbdev_generic.c

@@ -65,6 +65,8 @@ static void drm_fbdev_fb_destroy(struct fb_info *info)
 
 	drm_client_framebuffer_delete(fb_helper->buffer);
 	drm_client_release(&fb_helper->client);
+
+	drm_fb_helper_unprepare(fb_helper);
 	kfree(fb_helper);
 }
 

drivers/gpu/drm/exynos/exynos_drm_fbdev.c

@@ -183,8 +183,8 @@ int exynos_drm_fbdev_init(struct drm_device *dev)
 
 err_setup:
 	drm_fb_helper_fini(helper);
-
 err_init:
+	drm_fb_helper_unprepare(helper);
 	private->fb_helper = NULL;
 	kfree(fbdev);
 
@@ -219,6 +219,7 @@ void exynos_drm_fbdev_fini(struct drm_device *dev)
 	fbdev = to_exynos_fbdev(private->fb_helper);
 
 	exynos_drm_fbdev_destroy(dev, private->fb_helper);
+	drm_fb_helper_unprepare(private->fb_helper);
 	kfree(fbdev);
 	private->fb_helper = NULL;
 }

drivers/gpu/drm/gma500/framebuffer.c

@@ -427,6 +427,7 @@ int psb_fbdev_init(struct drm_device *dev)
 fini:
 	drm_fb_helper_fini(fb_helper);
 free:
+	drm_fb_helper_unprepare(fb_helper);
 	kfree(fb_helper);
 	return ret;
 }
@@ -439,6 +440,7 @@ static void psb_fbdev_fini(struct drm_device *dev)
 		return;
 
 	psb_fbdev_destroy(dev, dev_priv->fb_helper);
+	drm_fb_helper_unprepare(dev_priv->fb_helper);
 	kfree(dev_priv->fb_helper);
 	dev_priv->fb_helper = NULL;
 }

drivers/gpu/drm/i915/display/intel_fbdev.c

@@ -340,6 +340,7 @@ static void intel_fbdev_destroy(struct intel_fbdev *ifbdev)
 	if (ifbdev->fb)
 		drm_framebuffer_remove(&ifbdev->fb->base);
 
+	drm_fb_helper_unprepare(&ifbdev->helper);
 	kfree(ifbdev);
 }
 

drivers/gpu/drm/msm/msm_fbdev.c

@@ -170,6 +170,7 @@ struct drm_fb_helper *msm_fbdev_init(struct drm_device *dev)
 fini:
 	drm_fb_helper_fini(helper);
 fail:
+	drm_fb_helper_unprepare(helper);
 	kfree(fbdev);
 	return NULL;
 }
@@ -196,6 +197,7 @@ void msm_fbdev_free(struct drm_device *dev)
 		drm_framebuffer_remove(fbdev->fb);
 	}
 
+	drm_fb_helper_unprepare(helper);
 	kfree(fbdev);
 
 	priv->fbdev = NULL;

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;

drivers/gpu/drm/radeon/radeon_fb.c

@@ -367,6 +367,7 @@ int radeon_fbdev_init(struct radeon_device *rdev)
 fini:
 	drm_fb_helper_fini(&rfbdev->helper);
 free:
+	drm_fb_helper_unprepare(&rfbdev->helper);
 	kfree(rfbdev);
 	return ret;
 }
@@ -377,6 +378,7 @@ void radeon_fbdev_fini(struct radeon_device *rdev)
 		return;
 
 	radeon_fbdev_destroy(rdev->ddev, rdev->mode_info.rfbdev);
+	drm_fb_helper_unprepare(&rdev->mode_info.rfbdev->helper);
 	kfree(rdev->mode_info.rfbdev);
 	rdev->mode_info.rfbdev = NULL;
 }

drivers/gpu/drm/tegra/fb.c

@@ -315,6 +315,7 @@ static struct tegra_fbdev *tegra_fbdev_create(struct drm_device *drm)
 
 static void tegra_fbdev_free(struct tegra_fbdev *fbdev)
 {
+	drm_fb_helper_unprepare(&fbdev->base);
 	kfree(fbdev);
 }