drm/fbdev: Clamp fbdev surface size if too large

Clamp the fbdev surface size of the available maximumi height to avoid
failing to init console emulation. An example error is shown below.

  bad framebuffer height 2304, should be >= 768 && <= 768
  [drm] Initialized simpledrm 1.0.0 20200625 for simple-framebuffer.0 on minor 0
  simple-framebuffer simple-framebuffer.0: [drm] *ERROR* fbdev: Failed to setup generic emulation (ret=-22)

This is especially a problem with drivers that have very small screen
sizes and cannot over-allocate at all.

v2:
	* reduce warning level (Ville)
Signed-off-by: NThomas Zimmermann <tzimmermann@suse.de>
Fixes: 11e8f5fd ("drm: Add simpledrm driver")
Reviewed-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: NAlex Deucher <alexander.deucher@amd.com>
Reported-by: NAmanoel Dawod <kernel@amanoeldawod.com>
Reported-by: NZoltán Kővágó <dirty.ice.hu@gmail.com>
Reported-by: NMichael Stapelberg <michael+lkml@stapelberg.ch>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Maxime Ripard <maxime@cerno.tech>
Cc: dri-devel@lists.freedesktop.org
Cc: <stable@vger.kernel.org> # v5.14+
Link: https://patchwork.freedesktop.org/patch/msgid/20211005070355.7680-1-tzimmermann@suse.deSigned-off-by: NDave Airlie <airlied@redhat.com>

drivers/gpu/drm/drm_fb_helper.c

@@ -1506,6 +1506,7 @@ static int drm_fb_helper_single_fb_probe(struct drm_fb_helper *fb_helper,
 {
 	struct drm_client_dev *client = &fb_helper->client;
 	struct drm_device *dev = fb_helper->dev;
+	struct drm_mode_config *config = &dev->mode_config;
 	int ret = 0;
 	int crtc_count = 0;
 	struct drm_connector_list_iter conn_iter;
@@ -1663,6 +1664,11 @@ static int drm_fb_helper_single_fb_probe(struct drm_fb_helper *fb_helper,
 	/* Handle our overallocation */
 	sizes.surface_height *= drm_fbdev_overalloc;
 	sizes.surface_height /= 100;
+	if (sizes.surface_height > config->max_height) {
+		drm_dbg_kms(dev, "Fbdev over-allocation too large; clamping height to %d\n",
+			    config->max_height);
+		sizes.surface_height = config->max_height;
+	}
 
 	/* push down into drivers */
 	ret = (*fb_helper->funcs->fb_probe)(fb_helper, &sizes);