[PATCH 00/10] fbcon,fonts: Refactor framebuffer console rotation

Thomas Zimmermann
2026-03-27T13:04:37Z

Refactor the framebuffer console rotation into individual components
for glyphs, fonts and the overall fbcon state. Right now this is mixed
up in fbcon_rotate.{c,h}. Also build cursor rotation on top of the new
interfaces.

Start with an OOB fix in patch 1. If buffer allocation fails, fbcon
currently uses a too-small glyph buffer for output. Avoid that.

Patches 2 to 4 make a number of small improvements to the font library
and its callers.

Patches 5 to 8 refactor the font rotation. Fbcon rotation rotates each
individual glphy in a font buffer and uses the rotated buffer's glyphs
for output. The result looks like the console buffer has been rotated
as a whole. Split this into helpers that rotate individual glyphs and
a helper that rotates the font buffer of these. Then reimplement fbcon
rotation on top. Document the public font helpers.

Patch 9 rebuilds cursor rotation on top of the new glyph helpers. The
fbcon cursor is itself a glyph that has to be rotated in sync with the
font.

Patch 10 moves the state of fbcon rotation into a single place and makes
is a build-time conditional.

Tested with fbcon under bochs on Qemu.

Built upon the fbcon changes at [1].

[1] https://lore.kernel.org/linux-fbdev/20260309141723.137364-1-tzimmermann@suse.de/

Thomas Zimmermann (10):
fbcon: Avoid OOB font access if console rotation fails
vt: Implement helpers for struct vc_font in source file
lib/fonts: Provide helpers for calculating glyph pitch and size
lib/fonts: Clean up Makefile
lib/fonts: Implement glyph rotation
lib/fonts: Refactor glyph-pattern helpers
lib/fonts: Refactor glyph-rotation helpers
lib/fonts: Implement font rotation
fbcon: Fill cursor mask in helper function
fbcon: Put font-rotation state into separate struct

drivers/tty/vt/vt.c | 34 +++
drivers/video/fbdev/core/bitblit.c | 35 +--
drivers/video/fbdev/core/fbcon.c | 48 ++++-
drivers/video/fbdev/core/fbcon.h | 14 +-
drivers/video/fbdev/core/fbcon_ccw.c | 70 ++----
drivers/video/fbdev/core/fbcon_cw.c | 70 ++----
drivers/video/fbdev/core/fbcon_rotate.c | 88 ++------
drivers/video/fbdev/core/fbcon_rotate.h | 71 ------
drivers/video/fbdev/core/fbcon_ud.c | 67 ++----
include/linux/console_struct.h | 30 +--
include/linux/font.h | 51 +++++
lib/fonts/Makefile | 36 ++--
lib/fonts/font_rotate.c | 275 ++++++++++++++++++++++++
lib/fonts/fonts.c | 2 +-
14 files changed, 525 insertions(+), 366 deletions(-)
create mode 100644 lib/fonts/font_rotate.c

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2.53.0