lib/fonts: Store font data as font_data_t; update consoles

Store font data as pointer to font_data_t instead of unsigned char.
Update consoles.

Pointers to font data refer to the raw data. There is a hidden header
before the data that contains additional state. Document the existing
layout and semantics of font_data_t.

The data field in struct vc_font can be used by any console. Therefore
it still points to plain data without the additional header. Fbcon sets
its value from struct fbcon_display.fontdata. Hence, update the size
test in fbcon_resize() to use struct fbcon_display.fontdata instead of
struct vc_font.data.

v3:
- fix typos (Helge)
v2:
- 'Font lookup' -> 'Font description' in <linux/font.h>

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Helge Deller <deller@gmx.de>

1 files changed, 46 insertions, 1 deletions

diff --git a/include/linux/font.h b/include/linux/font.h
index d929c5fa32ca..746a0996a018 100644
--- a/include/linux/font.h
+++ b/include/linux/font.h
@@ -13,12 +13,57 @@
 
 #include <linux/types.h>
 
+/*
+ * font_data_t and helpers
+ */
+
+/**
+ * font_data_t - Raw font data
+ *
+ * Values of type font_data_t store a pointer to raw font data. The format
+ * is monochrome. Each bit sets a pixel of a stored glyph. Font data does
+ * not store geometry information for the individual glyphs. Users of the
+ * font have to store glyph size, pitch and character count separately.
+ *
+ * Font data in font_data_t is not equivalent to raw u8. Each pointer stores
+ * an additional hidden header before the font data. The layout is
+ *
+ * +------+-----------------------------+
+ * | -16  |  CRC32 Checksum (optional)  |
+ * | -12  |  <Unused>                   |
+ * |  -8  |  Number of data bytes       |
+ * |  -4  |  Reference count            |
+ * +------+-----------------------------+
+ * |   0  |  Data buffer                |
+ * |  ... |                             |
+ * +------+-----------------------------+
+ *
+ * Use helpers to access font_data_t. Use font_data_buf() to get the stored data.
+ */
+typedef const unsigned char font_data_t;
+
+/**
+ * font_data_buf() - Returns the font data as raw bytes
+ * @fd: The font data
+ *
+ * Returns:
+ * The raw font data. The provided buffer is read-only.
+ */
+static inline const unsigned char *font_data_buf(font_data_t *fd)
+{
+	return (const unsigned char *)fd;
+}
+
+/*
+ * Font description
+ */
+
 struct font_desc {
     int idx;
     const char *name;
     unsigned int width, height;
     unsigned int charcount;
-    const void *data;
+    font_data_t *data;
     int pref;
 };