[PATCH] drm/i915/fbdev: Preserve visible size when reusing BIOS fb

[Zheyu Shen <arsdragonfly@gmail.com>]

When reusing the BIOS framebuffer, intel_fbdev_driver_fbdev_probe()
overwrites sizes->fb_width and sizes->fb_height with the framebuffer's
dimensions. These become the visible fbdev resolution.

If the BIOS framebuffer is larger than the mode selected by the fbdev
client, fbcon consequently uses more rows and columns than are visible,
leaving console output outside the scanned-out area.

This occurs on a Broxton ZimaBlade 7700 with an MPI5001 panel connected
through DP-2 via PCON. The firmware provides a 1280x1024 framebuffer,
while i915 selects the panel's preferred 800x480 mode.

Keep the visible size requested by the fb helper. The larger BIOS
framebuffer is still reused, with its dimensions exposed through
xres_virtual and yres_virtual. This matches the fresh-allocation path,
which also preserves the requested visible size.

Boot-tested on the affected hardware: console output now displays
correctly while the virtual framebuffer remains 1280x1024.

Claude (claude-opus-5-5) assisted with patch preparation. Copilot assisted
with commit-message preparation, building, deployment, and validation.

Fixes: d978ef14456a ("drm/i915: Wrap the preallocated BIOS framebuffer and preserve for KMS fbcon v12")
Cc: stable@vger.kernel.org

Signed-off-by: Zheyu Shen <arsdragonfly@gmail.com>
---
 drivers/gpu/drm/i915/display/intel_fbdev.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_fbdev.c b/drivers/gpu/drm/i915/display/intel_fbdev.c
index 219ee17de3f6..5c043172a35c 100644
--- a/drivers/gpu/drm/i915/display/intel_fbdev.c
+++ b/drivers/gpu/drm/i915/display/intel_fbdev.c
@@ -324,8 +324,6 @@ int intel_fbdev_driver_fbdev_probe(struct drm_fb_helper *helper,
 	} else {
 		drm_dbg_kms(display->drm, "re-using BIOS fb\n");
 		prealloc = true;
-		sizes->fb_width = fb->base.width;
-		sizes->fb_height = fb->base.height;
 	}
 
 	obj = intel_fb_bo(&fb->base);
-- 
2.56.0