drm/vc4: plane: protect device resources after removal

(Hardware) resources which are bound to the driver and device lifecycle
must not be accessed after the device and driver are unbound.

However, the DRM device isn't freed as long as the last user closed it,
hence userspace can still call into the driver.

Therefore protect the critical sections which are accessing those
resources with drm_dev_enter() and drm_dev_exit().

Fixes: 9872c7a3 ("drm/vc4: plane: Switch to drmm_universal_plane_alloc()")
Signed-off-by: Danilo Krummrich <dakr@redhat.com>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://lore.kernel.org/r/20220824161327.330627-3-dakr@redhat.com

drivers/gpu/drm/vc4/vc4_plane.c

@@ -19,6 +19,7 @@
 #include <drm/drm_atomic_helper.h>
 #include <drm/drm_atomic_uapi.h>
 #include <drm/drm_blend.h>
+#include <drm/drm_drv.h>
 #include <drm/drm_fb_dma_helper.h>
 #include <drm/drm_fourcc.h>
 #include <drm/drm_framebuffer.h>
@@ -1219,6 +1220,10 @@ u32 vc4_plane_write_dlist(struct drm_plane *plane, u32 __iomem *dlist)
 {
 	struct vc4_plane_state *vc4_state = to_vc4_plane_state(plane->state);
 	int i;
+	int idx;
+
+	if (!drm_dev_enter(plane->dev, &idx))
+		goto out;
 
 	vc4_state->hw_dlist = dlist;
 
@@ -1226,6 +1231,9 @@ u32 vc4_plane_write_dlist(struct drm_plane *plane, u32 __iomem *dlist)
 	for (i = 0; i < vc4_state->dlist_count; i++)
 		writel(vc4_state->dlist[i], &dlist[i]);
 
+	drm_dev_exit(idx);
+
+out:
 	return vc4_state->dlist_count;
 }
 
@@ -1245,6 +1253,10 @@ void vc4_plane_async_set_fb(struct drm_plane *plane, struct drm_framebuffer *fb)
 	struct vc4_plane_state *vc4_state = to_vc4_plane_state(plane->state);
 	struct drm_gem_dma_object *bo = drm_fb_dma_get_gem_obj(fb, 0);
 	uint32_t addr;
+	int idx;
+
+	if (!drm_dev_enter(plane->dev, &idx))
+		return;
 
 	/* We're skipping the address adjustment for negative origin,
 	 * because this is only called on the primary plane.
@@ -1263,6 +1275,8 @@ void vc4_plane_async_set_fb(struct drm_plane *plane, struct drm_framebuffer *fb)
 	 * also use our updated address.
 	 */
 	vc4_state->dlist[vc4_state->ptr0_offset] = addr;
+
+	drm_dev_exit(idx);
 }
 
 static void vc4_plane_atomic_async_update(struct drm_plane *plane,
@@ -1271,6 +1285,10 @@ static void vc4_plane_atomic_async_update(struct drm_plane *plane,
 	struct drm_plane_state *new_plane_state = drm_atomic_get_new_plane_state(state,
 										 plane);
 	struct vc4_plane_state *vc4_state, *new_vc4_state;
+	int idx;
+
+	if (!drm_dev_enter(plane->dev, &idx))
+		return;
 
 	swap(plane->state->fb, new_plane_state->fb);
 	plane->state->crtc_x = new_plane_state->crtc_x;
@@ -1333,6 +1351,8 @@ static void vc4_plane_atomic_async_update(struct drm_plane *plane,
 	       &vc4_state->hw_dlist[vc4_state->pos2_offset]);
 	writel(vc4_state->dlist[vc4_state->ptr0_offset],
 	       &vc4_state->hw_dlist[vc4_state->ptr0_offset]);
+
+	drm_dev_exit(idx);
 }
 
 static int vc4_plane_atomic_async_check(struct drm_plane *plane,