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 glyph 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 all state of fbcon rotation into a single place and makes
it a build-time conditional.

Tested with fbcon under bochs on Qemu.

Built upon the fbcon changes at [1].

v2:
- fix sparse truncated-bits warning
- improve font sorting in Makefile
- fix typos

[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