[PATCH v2 08/10] lib/fonts: Implement font rotation

Thomas Zimmermann
2026-04-07T09:26:19Z

Move the core of fbcon's font-rotation code to the font library as
the new helper font_data_rotate(). The code can rotate in steps of
90°. For completeness, it also copies the glyph data for multiples
of 360°.

Bring back the memset optimization. A memset to 0 again clears the
whole glyph output buffer. Then use the internal rotation helpers on
the cleared output. Fbcon's original implementation worked like this,
but lost it during refactoring.

Replace fbcon's font-rotation code with the new implementations.
All that's left to do for fbcon is to maintain its internal fbcon
state.

v2:
- fix typos

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
---
drivers/video/fbdev/core/fbcon.h | 2 +-
drivers/video/fbdev/core/fbcon_rotate.c | 78 +++++-------------
include/linux/font.h | 3 +
lib/fonts/font_rotate.c | 103 ++++++++++++++++++++++++
4 files changed, 126 insertions(+), 60 deletions(-)

diff --git a/drivers/video/fbdev/core/fbcon.h b/drivers/video/fbdev/core/fbcon.h
index 1e3c1ef84762..1793f34a6c84 100644
--- a/drivers/video/fbdev/core/fbcon.h
+++ b/drivers/video/fbdev/core/fbcon.h
@@ -86,7 +86,7 @@ struct fbcon_par {
const u8 *fontdata;
u8 *cursor_src;
u32 cursor_size;
- u32 fd_size;
+ size_t fd_size;

const struct fbcon_bitops *bitops;
};
diff --git a/drivers/video/fbdev/core/fbcon_rotate.c b/drivers/video/fbdev/core/fbcon_rotate.c
index 588dc9d6758a..74206f5a6e98 100644
--- a/drivers/video/fbdev/core/fbcon_rotate.c
+++ b/drivers/video/fbdev/core/fbcon_rotate.c
@@ -8,84 +8,44 @@
* more details.
*/

-#include <linux/module.h>
-#include <linux/slab.h>
-#include <linux/string.h>
+#include <linux/errno.h>
#include <linux/fb.h>
#include <linux/font.h>
-#include <linux/vt_kern.h>
-#include <linux/console.h>
-#include <asm/types.h>
+
#include "fbcon.h"
#include "fbcon_rotate.h"

int fbcon_rotate_font(struct fb_info *info, struct vc_data *vc)
{
struct fbcon_par *par = info->fbcon_par;
- int len, err = 0;
- int s_cellsize, d_cellsize, i;
- const u8 *src;
- u8 *dst;
+ unsigned char *fontbuffer;
+ int ret;

if (vc->vc_font.data == par->fontdata &&
par->p->con_rotate == par->cur_rotate)
- goto finished;
+ return 0;

- src = par->fontdata = vc->vc_font.data;
+ par->fontdata = vc->vc_font.data;
par->cur_rotate = par->p->con_rotate;
- len = vc->vc_font.charcount;
- s_cellsize = font_glyph_size(vc->vc_font.width, vc->vc_font.height);
- d_cellsize = s_cellsize;
-
- if (par->rotate == FB_ROTATE_CW ||
- par->rotate == FB_ROTATE_CCW)
- d_cellsize = font_glyph_size(vc->vc_font.height, vc->vc_font.width);

if (info->fbops->fb_sync)
info->fbops->fb_sync(info);

- if (par->fd_size < d_cellsize * len) {
- kfree(par->fontbuffer);
- par->fontbuffer = NULL;
- par->fd_size = 0;
-
- dst = kmalloc_array(len, d_cellsize, GFP_KERNEL);
-
- if (dst == NULL) {
- err = -ENOMEM;
- goto finished;
- }
-
- par->fd_size = d_cellsize * len;
- par->fontbuffer = dst;
+ fontbuffer = font_data_rotate(par->p->fontdata, vc->vc_font.width,
+ vc->vc_font.height, vc->vc_font.charcount,
+ par->rotate, par->fontbuffer, &par->fd_size);
+ if (IS_ERR(fontbuffer)) {
+ ret = PTR_ERR(fontbuffer);
+ goto err_kfree;
}

- dst = par->fontbuffer;
+ par->fontbuffer = fontbuffer;

- switch (par->rotate) {
- case FB_ROTATE_UD:
- for (i = len; i--; ) {
- font_glyph_rotate_180(src, vc->vc_font.width, vc->vc_font.height, dst);
- src += s_cellsize;
- dst += d_cellsize;
- }
- break;
- case FB_ROTATE_CW:
- for (i = len; i--; ) {
- font_glyph_rotate_90(src, vc->vc_font.width, vc->vc_font.height, dst);
- src += s_cellsize;
- dst += d_cellsize;
- }
- break;
- case FB_ROTATE_CCW:
- for (i = len; i--; ) {
- font_glyph_rotate_270(src, vc->vc_font.width, vc->vc_font.height, dst);
- src += s_cellsize;
- dst += d_cellsize;
- }
- break;
- }
+ return 0;
+
+err_kfree:
+ kfree(par->fontbuffer);
+ par->fontbuffer = NULL; /* clear here to avoid output */

-finished:
- return err;
+ return ret;
}
diff --git a/include/linux/font.h b/include/linux/font.h
index 0a240dd70422..6845f02d739a 100644
--- a/include/linux/font.h
+++ b/include/linux/font.h
@@ -111,6 +111,9 @@ void font_glyph_rotate_180(const unsigned char *glyph, unsigned int width, unsig
unsigned char *out);
void font_glyph_rotate_270(const unsigned char *glyph, unsigned int width, unsigned int height,
unsigned char *out);
+unsigned char *font_data_rotate(font_data_t *fd, unsigned int width, unsigned int height,
+ unsigned int charcount, unsigned int steps,
+ unsigned char *buf, size_t *bufsize);

/*
* Font description
diff --git a/lib/fonts/font_rotate.c b/lib/fonts/font_rotate.c
index 09f6218e036f..065e0fc0667b 100644
--- a/lib/fonts/font_rotate.c
+++ b/lib/fonts/font_rotate.c
@@ -9,8 +9,11 @@
* more details.
*/

+#include <linux/errno.h>
#include <linux/export.h>
#include <linux/math.h>
+#include <linux/overflow.h>
+#include <linux/slab.h>
#include <linux/string.h>

#include "font.h"
@@ -170,3 +173,103 @@ void font_glyph_rotate_270(const unsigned char *glyph, unsigned int width, unsig
__font_glyph_rotate_270(glyph, width, height, out);
}
EXPORT_SYMBOL_GPL(font_glyph_rotate_270);
+
+/**
+ * font_data_rotate - Rotate font data by multiples of 90°
+ * @fd: The font data to rotate
+ * @width: The glyph width in bits per scanline
+ * @height: The number of scanlines in the glyph
+ * @charcount: The number of glyphs in the font
+ * @steps: Number of rotation steps of 90°
+ * @buf: Preallocated output buffer; can be NULL
+ * @bufsize: The size of @buf in bytes; can be NULL
+ *
+ * The parameters @width and @height refer to the visible number of pixels
+ * and scanlines in a single glyph. The number of glyphs is given in @charcount.
+ * Rotation happens in steps of 90°. The @steps parameter can have any value,
+ * but only 0 to 3 produce distinct results. With 4 or higher, a full rotation
+ * has been performed. You can pass any value for @steps and the helper will
+ * perform the appropriate rotation. Note that the returned buffer is not
+ * compatible with font_data_t. It only contains glyph data in the same format
+ * as returned by font_data_buf(). Callers are responsible to free the returned
+ * buffer with kfree(). Font rotation typically happens when displays get
+ * re-oriented. To avoid unnecessary re-allocation of the memory buffer, the
+ * caller can pass in an earlier result buffer in @buf for reuse. The old and
+ * new buffer sizes are given and retrieved by the caller in @bufsize. The
+ * allocation semantics are compatible with krealloc().
+ *
+ * Returns:
+ * A buffer with rotated glyphs on success, or an error pointer otherwise
+ */
+unsigned char *font_data_rotate(font_data_t *fd, unsigned int width, unsigned int height,
+ unsigned int charcount, unsigned int steps,
+ unsigned char *buf, size_t *bufsize)
+{
+ const unsigned char *src = font_data_buf(fd);
+ unsigned int s_cellsize = font_glyph_size(width, height);
+ unsigned int d_cellsize, i;
+ unsigned char *dst;
+ size_t size;
+
+ steps %= 4;
+
+ switch (steps) {
+ case 0:
+ case 2:
+ d_cellsize = s_cellsize;
+ break;
+ case 1:
+ case 3:
+ d_cellsize = font_glyph_size(height, width); /* flip width/height */
+ break;
+ }
+
+ if (check_mul_overflow(charcount, d_cellsize, &size))
+ return ERR_PTR(-EINVAL);
+
+ if (!buf || !bufsize || size > *bufsize) {
+ dst = kmalloc_array(charcount, d_cellsize, GFP_KERNEL);
+ if (!dst)
+ return ERR_PTR(-ENOMEM);
+
+ kfree(buf);
+ buf = dst;
+ if (bufsize)
+ *bufsize = size;
+ } else {
+ dst = buf;
+ }
+
+ switch (steps) {
+ case 0:
+ memcpy(dst, src, size);
+ break;
+ case 1:
+ memset(dst, 0, size);
+ for (i = 0; i < charcount; ++i) {
+ __font_glyph_rotate_90(src, width, height, dst);
+ src += s_cellsize;
+ dst += d_cellsize;
+ }
+ break;
+ case 2:
+ memset(dst, 0, size);
+ for (i = 0; i < charcount; ++i) {
+ __font_glyph_rotate_180(src, width, height, dst);
+ src += s_cellsize;
+ dst += d_cellsize;
+ }
+ break;
+ case 3:
+ memset(dst, 0, size);
+ for (i = 0; i < charcount; ++i) {
+ __font_glyph_rotate_270(src, width, height, dst);
+ src += s_cellsize;
+ dst += d_cellsize;
+ }
+ break;
+ }
+
+ return buf;
+}
+EXPORT_SYMBOL_GPL(font_data_rotate);
--
2.53.0