[PATCH 20/23] [DO NOT MERGE] drm/format-helper: Add font-support for DRM pixmap

[Thomas Zimmermann]

Add support for blitting characters. An instance of struct font_desc
stores the the character shapes. The blitting source pixmap contains
a reference to a character's glyph, which can then be blitted to the
destination. drm_pixmap_init_from_font_desc() sets up the pixmap.

  struct drm_pixmap;

  drm_pixmap_init_from_font_desc(&drm_pixmap, font_desc, font_data, 'c');
  drm_fb_blit(..., &pixmap, ...); // blits the character 'c'

To blit a string of characters, drm_pixmap_set_font_char() updates
the character's value.

  struct drm_pixmap;
  const char *str = "Hello world!"

  drm_pixmap_init_from_font_desc(&drm_pixmap, font_desc, font_data, '\0');

  while (*str) {
    drm_pixmap_set_font_char(&pixmap, font_data, *str);
    drm_fb_blit(..., &pixmap, ...); // blits *str
    ++str;
  }

Further helpers can be build from these primitives.

Signed-off-by: Thomas Zimmermann <tzimmermann at suse.de>
---
 drivers/gpu/drm/drm_format_helper.c | 27 +++++++++++++++++++++++++++
 include/drm/drm_format_helper.h     |  4 ++++
 2 files changed, 31 insertions(+)

diff --git a/drivers/gpu/drm/drm_format_helper.c b/drivers/gpu/drm/drm_format_helper.c
index 6b80be55cc5c0..ed90745f4d9fb 100644
--- a/drivers/gpu/drm/drm_format_helper.c
+++ b/drivers/gpu/drm/drm_format_helper.c
@@ -8,6 +8,7 @@
  * (at your option) any later version.
  */
 
+#include <linux/font.h>
 #include <linux/io.h>
 #include <linux/iosys-map.h>
 #include <linux/module.h>
@@ -181,6 +182,32 @@ void drm_pixmap_init_from_framebuffer(struct drm_pixmap *pix, const struct drm_f
 }
 EXPORT_SYMBOL(drm_pixmap_init_from_framebuffer);
 
+void drm_pixmap_init_from_font_desc(struct drm_pixmap *pix, const struct font_desc *font,
+				    const struct iosys_map *data, int c)
+{
+	const struct drm_rect clip = DRM_RECT_INIT(0, 0, font->width, font->height);
+	const struct drm_format_info *format = drm_format_info(DRM_FORMAT_C1);
+	const unsigned int pitches[DRM_FORMAT_MAX_PLANES] = {
+		drm_format_info_min_pitch(format, 0, font->width),
+	};
+	struct iosys_map cdata[DRM_FORMAT_MAX_PLANES] = {
+		IOSYS_MAP_INIT_OFFSET(&data[0], c * font->height * pitches[0]),
+	};
+
+	drm_pixmap_init(pix, format, cdata, pitches, &clip);
+}
+EXPORT_SYMBOL(drm_pixmap_init_from_font_desc);
+
+void drm_pixmap_set_font_char(struct drm_pixmap *pix, const struct iosys_map *data, int c)
+{
+	unsigned int height = drm_rect_height(&pix->clip);
+	size_t i;
+
+	for (i = 0; i < pix->format->num_planes; ++i)
+		pix->data[i] = IOSYS_MAP_INIT_OFFSET(&data[i], c * height * pix->pitches[i]);
+}
+EXPORT_SYMBOL(drm_pixmap_set_font_char);
+
 static int __drm_fb_xfrm(void *dst, unsigned long dst_pitch, unsigned long dst_pixsize,
 			 const void *src, unsigned long src_pitch, unsigned long src_pixsize,
 			 const struct drm_rect *src_clip, bool src_cached_hint,
diff --git a/include/drm/drm_format_helper.h b/include/drm/drm_format_helper.h
index a78360e229a45..098e6f8412465 100644
--- a/include/drm/drm_format_helper.h
+++ b/include/drm/drm_format_helper.h
@@ -14,6 +14,7 @@
 
 struct drm_device;
 struct drm_framebuffer;
+struct font_desc;
 
 /**
  * struct drm_format_conv_state - Stores format-conversion state
@@ -93,6 +94,9 @@ struct drm_pixmap {
 
 void drm_pixmap_init_from_framebuffer(struct drm_pixmap *pix, const struct drm_framebuffer *fb,
 				      const struct iosys_map *data, const struct drm_rect *clip);
+void drm_pixmap_init_from_font_desc(struct drm_pixmap *pix, const struct font_desc *font,
+				    const struct iosys_map *data, int c);
+void drm_pixmap_set_font_char(struct drm_pixmap *pix, const struct iosys_map *data, int c);
 
 unsigned int drm_fb_clip_offset(unsigned int pitch, const struct drm_format_info *format,
 				const struct drm_rect *clip);
-- 
2.43.0