drm/tinydrm: Use drm_dev_enter/exit()

This protects device resources from use after device removal.

There are 3 ways for driver-device unbinding to happen:
- The driver module is unloaded causing the driver to be unregistered.
  This can't happen as long as there are open file handles because a
  reference is taken on the module.
- The device is removed (Device Tree overlay unloading).
  This can happen at any time.
- The driver sysfs unbind file can be used to unbind the driver from the
  device. This can happen any time.

v2: Since drm_atomic_helper_shutdown() has to be called after
    drm_dev_unplug() we don't want do block ->disable after unplug.

Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
Acked-by: Gerd Hoffmann <kraxel@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190225144232.20761-8-noralf@tronnes.org

1 files changed, 7 insertions, 2 deletions

diff --git a/drivers/gpu/drm/tinydrm/st7735r.c b/drivers/gpu/drm/tinydrm/st7735r.c
index 0f8a346026ac..022e9849b95b 100644
--- a/drivers/gpu/drm/tinydrm/st7735r.c
+++ b/drivers/gpu/drm/tinydrm/st7735r.c
@@ -44,14 +44,17 @@ static void jd_t18003_t01_pipe_enable(struct drm_simple_display_pipe *pipe,
 				      struct drm_plane_state *plane_state)
 {
 	struct mipi_dbi *mipi = drm_to_mipi_dbi(pipe->crtc.dev);
-	int ret;
+	int ret, idx;
 	u8 addr_mode;
 
+	if (!drm_dev_enter(pipe->crtc.dev, &idx))
+		return;
+
 	DRM_DEBUG_KMS("\n");
 
 	ret = mipi_dbi_poweron_reset(mipi);
 	if (ret)
-		return;
+		goto out_exit;
 
 	msleep(150);
 
@@ -102,6 +105,8 @@ static void jd_t18003_t01_pipe_enable(struct drm_simple_display_pipe *pipe,
 	msleep(20);
 
 	mipi_dbi_enable_flush(mipi, crtc_state, plane_state);
+out_exit:
+	drm_dev_exit(idx);
 }
 
 static const struct drm_simple_display_pipe_funcs jd_t18003_t01_pipe_funcs = {