[PATCH] drm/fbdev: Clamp fbdev surface size if too large

Thomas Zimmermann tzimmermann at suse.de
Mon Oct 4 08:15:06 UTC 2021


Clamp the fbdev surface size of the available maximum 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.

Signed-off-by: Thomas Zimmermann <tzimmermann at suse.de>
Fixes: 11e8f5fd223b ("drm: Add simpledrm driver")
Reported-by: Amanoel Dawod <kernel at amanoeldawod.com>
Reported-by: Zoltán Kővágó <dirty.ice.hu at gmail.com>
Reported-by: Michael Stapelberg <michael+lkml at stapelberg.ch>
Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
Cc: Maxime Ripard <maxime at cerno.tech>
Cc: dri-devel at lists.freedesktop.org
Cc: <stable at vger.kernel.org> # v5.14+
---
 drivers/gpu/drm/drm_fb_helper.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
index 6860223f0068..364f11900b37 100644
--- a/drivers/gpu/drm/drm_fb_helper.c
+++ b/drivers/gpu/drm/drm_fb_helper.c
@@ -1508,6 +1508,7 @@ 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;
@@ -1665,6 +1666,11 @@ 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_warn(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);
--
2.33.0



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