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: Thomas Zimmermann <tzimmermann@suse.de>
Fixes: 11e8f5fd223b ("drm: Add simpledrm driver")
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Reported-by: Amanoel Dawod <kernel@amanoeldawod.com>
Reported-by: Zoltán Kővágó <dirty.ice.hu@gmail.com>
Reported-by: Michael 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.de
Signed-off-by: Dave Airlie <airlied@redhat.com>
diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
index 3ab0783..8e7a124 100644
--- a/drivers/gpu/drm/drm_fb_helper.c
+++ b/drivers/gpu/drm/drm_fb_helper.c
@@ -1506,6 +1506,7 @@
 {
 	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 @@
 	/* 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);