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, 20 insertions, 3 deletions

diff --git a/drivers/gpu/drm/tinydrm/ili9225.c b/drivers/gpu/drm/tinydrm/ili9225.c
index 4d387a07c48b..0e9fde47b53b 100644
--- a/drivers/gpu/drm/tinydrm/ili9225.c
+++ b/drivers/gpu/drm/tinydrm/ili9225.c
@@ -89,13 +89,16 @@ static void ili9225_fb_dirty(struct drm_framebuffer *fb, struct drm_rect *rect)
 	bool swap = mipi->swap_bytes;
 	u16 x_start, y_start;
 	u16 x1, x2, y1, y2;
-	int ret = 0;
+	int idx, ret = 0;
 	bool full;
 	void *tr;
 
 	if (!mipi->enabled)
 		return;
 
+	if (!drm_dev_enter(fb->dev, &idx))
+		return;
+
 	full = width == fb->width && height == fb->height;
 
 	DRM_DEBUG_KMS("Flushing [FB:%d] " DRM_RECT_FMT "\n", fb->base.id, DRM_RECT_ARG(rect));
@@ -158,6 +161,8 @@ static void ili9225_fb_dirty(struct drm_framebuffer *fb, struct drm_rect *rect)
 err_msg:
 	if (ret)
 		dev_err_once(fb->dev->dev, "Failed to update display %d\n", ret);
+
+	drm_dev_exit(idx);
 }
 
 static void ili9225_pipe_update(struct drm_simple_display_pipe *pipe,
@@ -191,9 +196,12 @@ static void ili9225_pipe_enable(struct drm_simple_display_pipe *pipe,
 		.y1 = 0,
 		.y2 = fb->height,
 	};
-	int ret;
+	int ret, idx;
 	u8 am_id;
 
+	if (!drm_dev_enter(pipe->crtc.dev, &idx))
+		return;
+
 	DRM_DEBUG_KMS("\n");
 
 	mipi_dbi_hw_reset(mipi);
@@ -207,7 +215,7 @@ static void ili9225_pipe_enable(struct drm_simple_display_pipe *pipe,
 	ret = ili9225_command(mipi, ILI9225_POWER_CONTROL_1, 0x0000);
 	if (ret) {
 		DRM_DEV_ERROR(dev, "Error sending command %d\n", ret);
-		return;
+		goto out_exit;
 	}
 	ili9225_command(mipi, ILI9225_POWER_CONTROL_2, 0x0000);
 	ili9225_command(mipi, ILI9225_POWER_CONTROL_3, 0x0000);
@@ -280,6 +288,8 @@ static void ili9225_pipe_enable(struct drm_simple_display_pipe *pipe,
 
 	mipi->enabled = true;
 	ili9225_fb_dirty(fb, &rect);
+out_exit:
+	drm_dev_exit(idx);
 }
 
 static void ili9225_pipe_disable(struct drm_simple_display_pipe *pipe)
@@ -288,6 +298,13 @@ static void ili9225_pipe_disable(struct drm_simple_display_pipe *pipe)
 
 	DRM_DEBUG_KMS("\n");
 
+	/*
+	 * This callback is not protected by drm_dev_enter/exit since we want to
+	 * turn off the display on regular driver unload. It's highly unlikely
+	 * that the underlying SPI controller is gone should this be called after
+	 * unplug.
+	 */
+
 	if (!mipi->enabled)
 		return;