drm/vc4: crtc: 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: 7cc4214c ("drm/vc4: crtc: Switch to drmm_kzalloc")
Signed-off-by: Danilo Krummrich <dakr@redhat.com>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://lore.kernel.org/r/20220824161327.330627-4-dakr@redhat.com

drivers/gpu/drm/vc4/vc4_crtc.c

@@ -39,6 +39,7 @@
 #include <drm/drm_atomic_uapi.h>
 #include <drm/drm_fb_dma_helper.h>
 #include <drm/drm_framebuffer.h>
+#include <drm/drm_drv.h>
 #include <drm/drm_print.h>
 #include <drm/drm_probe_helper.h>
 #include <drm/drm_vblank.h>
@@ -295,10 +296,17 @@ struct drm_encoder *vc4_get_crtc_encoder(struct drm_crtc *crtc,
 static void vc4_crtc_pixelvalve_reset(struct drm_crtc *crtc)
 {
 	struct vc4_crtc *vc4_crtc = to_vc4_crtc(crtc);
+	struct drm_device *dev = crtc->dev;
+	int idx;
+
+	if (!drm_dev_enter(dev, &idx))
+		return;
 
 	/* The PV needs to be disabled before it can be flushed */
 	CRTC_WRITE(PV_CONTROL, CRTC_READ(PV_CONTROL) & ~PV_CONTROL_EN);
 	CRTC_WRITE(PV_CONTROL, CRTC_READ(PV_CONTROL) | PV_CONTROL_FIFO_CLR);
+
+	drm_dev_exit(idx);
 }
 
 static void vc4_crtc_config_pv(struct drm_crtc *crtc, struct drm_encoder *encoder,
@@ -321,6 +329,10 @@ static void vc4_crtc_config_pv(struct drm_crtc *crtc, struct drm_encoder *encode
 	u32 format = is_dsi1 ? PV_CONTROL_FORMAT_DSIV_24 : PV_CONTROL_FORMAT_24;
 	u8 ppc = pv_data->pixels_per_clock;
 	bool debug_dump_regs = false;
+	int idx;
+
+	if (!drm_dev_enter(dev, &idx))
+		return;
 
 	if (debug_dump_regs) {
 		struct drm_printer p = drm_info_printer(&vc4_crtc->pdev->dev);
@@ -410,6 +422,8 @@ static void vc4_crtc_config_pv(struct drm_crtc *crtc, struct drm_encoder *encode
 			 drm_crtc_index(crtc));
 		drm_print_regset32(&p, &vc4_crtc->regset);
 	}
+
+	drm_dev_exit(idx);
 }
 
 static void require_hvs_enabled(struct drm_device *dev)
@@ -430,7 +444,10 @@ static int vc4_crtc_disable(struct drm_crtc *crtc,
 	struct vc4_crtc *vc4_crtc = to_vc4_crtc(crtc);
 	struct drm_device *dev = crtc->dev;
 	struct vc4_dev *vc4 = to_vc4_dev(dev);
-	int ret;
+	int idx, ret;
+
+	if (!drm_dev_enter(dev, &idx))
+		return -ENODEV;
 
 	CRTC_WRITE(PV_V_CONTROL,
 		   CRTC_READ(PV_V_CONTROL) & ~PV_VCONTROL_VIDEN);
@@ -464,6 +481,8 @@ static int vc4_crtc_disable(struct drm_crtc *crtc,
 	if (vc4_encoder && vc4_encoder->post_crtc_powerdown)
 		vc4_encoder->post_crtc_powerdown(encoder, state);
 
+	drm_dev_exit(idx);
+
 	return 0;
 }
 
@@ -588,10 +607,14 @@ static void vc4_crtc_atomic_enable(struct drm_crtc *crtc,
 	struct vc4_crtc *vc4_crtc = to_vc4_crtc(crtc);
 	struct drm_encoder *encoder = vc4_get_crtc_encoder(crtc, new_state);
 	struct vc4_encoder *vc4_encoder = to_vc4_encoder(encoder);
+	int idx;
 
 	drm_dbg(dev, "Enabling CRTC %s (%u) connected to Encoder %s (%u)",
 		crtc->name, crtc->base.id, encoder->name, encoder->base.id);
 
+	if (!drm_dev_enter(dev, &idx))
+		return;
+
 	require_hvs_enabled(dev);
 
 	/* Enable vblank irq handling before crtc is started otherwise
@@ -619,6 +642,8 @@ static void vc4_crtc_atomic_enable(struct drm_crtc *crtc,
 
 	if (vc4_encoder->post_crtc_enable)
 		vc4_encoder->post_crtc_enable(encoder, state);
+
+	drm_dev_exit(idx);
 }
 
 static enum drm_mode_status vc4_crtc_mode_valid(struct drm_crtc *crtc,
@@ -711,17 +736,31 @@ static int vc4_crtc_atomic_check(struct drm_crtc *crtc,
 static int vc4_enable_vblank(struct drm_crtc *crtc)
 {
 	struct vc4_crtc *vc4_crtc = to_vc4_crtc(crtc);
+	struct drm_device *dev = crtc->dev;
+	int idx;
+
+	if (!drm_dev_enter(dev, &idx))
+		return -ENODEV;
 
 	CRTC_WRITE(PV_INTEN, PV_INT_VFP_START);
 
+	drm_dev_exit(idx);
+
 	return 0;
 }
 
 static void vc4_disable_vblank(struct drm_crtc *crtc)
 {
 	struct vc4_crtc *vc4_crtc = to_vc4_crtc(crtc);
+	struct drm_device *dev = crtc->dev;
+	int idx;
+
+	if (!drm_dev_enter(dev, &idx))
+		return;
 
 	CRTC_WRITE(PV_INTEN, 0);
+
+	drm_dev_exit(idx);
 }
 
 static void vc4_crtc_handle_page_flip(struct vc4_crtc *vc4_crtc)