drm/i915: Attach a fb to the load-detect pipe

We need to ensure that we feed valid memory into the display plane
attached to the pipe when switching the pipe on. Otherwise, the display
engine may read through an invalid PTE and so throw an PGTBL_ER
exception.

As we need to perform load detection before even the first object is
allocated for the fbdev, there is no pre-existing object large enough
for us to borrow to use as the framebuffer. So we need to create one
and cleanup afterwards. At other times, the current fbcon may be large
enough for us to borrow it for duration of load detection.

Found by assert_fb_bound_for_plane().

Reported-by: Knut Petersen <Knut_Petersen@t-online.de>
References: https://bugs.freedesktop.org/show_bug.cgi?id=36246
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Keith Packard <keithp@keithp.com>

drivers/gpu/drm/i915/intel_display.c

@@ -5481,6 +5481,92 @@ static struct drm_display_mode load_detect_mode = {
 		 704, 832, 0, 480, 489, 491, 520, 0, DRM_MODE_FLAG_NHSYNC | DRM_MODE_FLAG_NVSYNC),
 };
 
+static struct drm_framebuffer *
+intel_framebuffer_create(struct drm_device *dev,
+			 struct drm_mode_fb_cmd *mode_cmd,
+			 struct drm_i915_gem_object *obj)
+{
+	struct intel_framebuffer *intel_fb;
+	int ret;
+
+	intel_fb = kzalloc(sizeof(*intel_fb), GFP_KERNEL);
+	if (!intel_fb) {
+		drm_gem_object_unreference_unlocked(&obj->base);
+		return ERR_PTR(-ENOMEM);
+	}
+
+	ret = intel_framebuffer_init(dev, intel_fb, mode_cmd, obj);
+	if (ret) {
+		drm_gem_object_unreference_unlocked(&obj->base);
+		kfree(intel_fb);
+		return ERR_PTR(ret);
+	}
+
+	return &intel_fb->base;
+}
+
+static u32
+intel_framebuffer_pitch_for_width(int width, int bpp)
+{
+	u32 pitch = DIV_ROUND_UP(width * bpp, 8);
+	return ALIGN(pitch, 64);
+}
+
+static u32
+intel_framebuffer_size_for_mode(struct drm_display_mode *mode, int bpp)
+{
+	u32 pitch = intel_framebuffer_pitch_for_width(mode->hdisplay, bpp);
+	return ALIGN(pitch * mode->vdisplay, PAGE_SIZE);
+}
+
+static struct drm_framebuffer *
+intel_framebuffer_create_for_mode(struct drm_device *dev,
+				  struct drm_display_mode *mode,
+				  int depth, int bpp)
+{
+	struct drm_i915_gem_object *obj;
+	struct drm_mode_fb_cmd mode_cmd;
+
+	obj = i915_gem_alloc_object(dev,
+				    intel_framebuffer_size_for_mode(mode, bpp));
+	if (obj == NULL)
+		return ERR_PTR(-ENOMEM);
+
+	mode_cmd.width = mode->hdisplay;
+	mode_cmd.height = mode->vdisplay;
+	mode_cmd.depth = depth;
+	mode_cmd.bpp = bpp;
+	mode_cmd.pitch = intel_framebuffer_pitch_for_width(mode_cmd.width, bpp);
+
+	return intel_framebuffer_create(dev, &mode_cmd, obj);
+}
+
+static struct drm_framebuffer *
+mode_fits_in_fbdev(struct drm_device *dev,
+		   struct drm_display_mode *mode)
+{
+	struct drm_i915_private *dev_priv = dev->dev_private;
+	struct drm_i915_gem_object *obj;
+	struct drm_framebuffer *fb;
+
+	if (dev_priv->fbdev == NULL)
+		return NULL;
+
+	obj = dev_priv->fbdev->ifb.obj;
+	if (obj == NULL)
+		return NULL;
+
+	fb = &dev_priv->fbdev->ifb.base;
+	if (fb->pitch < intel_framebuffer_pitch_for_width(mode->hdisplay,
+							  fb->bits_per_pixel))
+		return NULL;
+
+	if (obj->base.size < mode->vdisplay * fb->pitch)
+		return NULL;
+
+	return fb;
+}
+
 bool intel_get_load_detect_pipe(struct intel_encoder *intel_encoder,
 				struct drm_connector *connector,
 				struct drm_display_mode *mode,
@@ -5491,8 +5577,13 @@ bool intel_get_load_detect_pipe(struct intel_encoder *intel_encoder,
 	struct drm_encoder *encoder = &intel_encoder->base;
 	struct drm_crtc *crtc = NULL;
 	struct drm_device *dev = encoder->dev;
+	struct drm_framebuffer *old_fb;
 	int i = -1;
 
+	DRM_DEBUG_KMS("[CONNECTOR:%d:%s], [ENCODER:%d:%s]\n",
+		      connector->base.id, drm_get_connector_name(connector),
+		      encoder->base.id, drm_get_encoder_name(encoder));
+
 	/*
 	 * Algorithm gets a little messy:
 	 *
@@ -5551,12 +5642,38 @@ bool intel_get_load_detect_pipe(struct intel_encoder *intel_encoder,
 	intel_crtc = to_intel_crtc(crtc);
 	old->dpms_mode = intel_crtc->dpms_mode;
 	old->load_detect_temp = true;
+	old->release_fb = NULL;
 
 	if (!mode)
 		mode = &load_detect_mode;
 
-	if (!drm_crtc_helper_set_mode(crtc, mode, 0, 0, crtc->fb)) {
+	old_fb = crtc->fb;
+
+	/* We need a framebuffer large enough to accommodate all accesses
+	 * that the plane may generate whilst we perform load detection.
+	 * We can not rely on the fbcon either being present (we get called
+	 * during its initialisation to detect all boot displays, or it may
+	 * not even exist) or that it is large enough to satisfy the
+	 * requested mode.
+	 */
+	crtc->fb = mode_fits_in_fbdev(dev, mode);
+	if (crtc->fb == NULL) {
+		DRM_DEBUG_KMS("creating tmp fb for load-detection\n");
+		crtc->fb = intel_framebuffer_create_for_mode(dev, mode, 24, 32);
+		old->release_fb = crtc->fb;
+	} else
+		DRM_DEBUG_KMS("reusing fbdev for load-detection framebuffer\n");
+	if (IS_ERR(crtc->fb)) {
+		DRM_DEBUG_KMS("failed to allocate framebuffer for load-detection\n");
+		crtc->fb = old_fb;
+		return false;
+	}
+
+	if (!drm_crtc_helper_set_mode(crtc, mode, 0, 0, old_fb)) {
 		DRM_DEBUG_KMS("failed to set mode on load-detect pipe\n");
+		if (old->release_fb)
+			old->release_fb->funcs->destroy(old->release_fb);
+		crtc->fb = old_fb;
 		return false;
 	}
 
@@ -5576,9 +5693,17 @@ void intel_release_load_detect_pipe(struct intel_encoder *intel_encoder,
 	struct drm_encoder_helper_funcs *encoder_funcs = encoder->helper_private;
 	struct drm_crtc_helper_funcs *crtc_funcs = crtc->helper_private;
 
+	DRM_DEBUG_KMS("[CONNECTOR:%d:%s], [ENCODER:%d:%s]\n",
+		      connector->base.id, drm_get_connector_name(connector),
+		      encoder->base.id, drm_get_encoder_name(encoder));
+
 	if (old->load_detect_temp) {
 		connector->encoder = NULL;
 		drm_helper_disable_unused_functions(dev);
+
+		if (old->release_fb)
+			old->release_fb->funcs->destroy(old->release_fb);
+
 		return;
 	}
 
@@ -6566,27 +6691,12 @@ intel_user_framebuffer_create(struct drm_device *dev,
 			      struct drm_mode_fb_cmd *mode_cmd)
 {
 	struct drm_i915_gem_object *obj;
-	struct intel_framebuffer *intel_fb;
-	int ret;
 
 	obj = to_intel_bo(drm_gem_object_lookup(dev, filp, mode_cmd->handle));
 	if (&obj->base == NULL)
 		return ERR_PTR(-ENOENT);
 
-	intel_fb = kzalloc(sizeof(*intel_fb), GFP_KERNEL);
-	if (!intel_fb) {
-		drm_gem_object_unreference_unlocked(&obj->base);
-		return ERR_PTR(-ENOMEM);
-	}
-
-	ret = intel_framebuffer_init(dev, intel_fb, mode_cmd, obj);
-	if (ret) {
-		drm_gem_object_unreference_unlocked(&obj->base);
-		kfree(intel_fb);
-		return ERR_PTR(ret);
-	}
-
-	return &intel_fb->base;
+	return intel_framebuffer_create(dev, mode_cmd, obj);
 }
 
 static const struct drm_mode_config_funcs intel_mode_funcs = {

drivers/gpu/drm/i915/intel_drv.h

@@ -292,6 +292,7 @@ extern void intel_wait_for_vblank(struct drm_device *dev, int pipe);
 extern void intel_wait_for_pipe_off(struct drm_device *dev, int pipe);
 
 struct intel_load_detect_pipe {
+	struct drm_framebuffer *release_fb;
 	bool load_detect_temp;
 	int dpms_mode;
 };