[PATCH v4 1/5] vt: Add cursor-size helpers

@@ -71,6 +71,7 @@
  * by Adam Tla/lka <atlka@pg.gda.pl>, Aug 2006
  */
 
+#include <linux/compiler.h>
 #include <linux/module.h>
 #include <linux/types.h>
 #include <linux/sched/signal.h>

@@ -264,6 +265,119 @@ unsigned int vc_font_size(const struct vc_font *font)
 }
 EXPORT_SYMBOL_GPL(vc_font_size);
 
+/*
+ * Cursors
+ */
+
+/**
+ * vc_cursor_valid_size - Computes a valid cursor size from the given value
+ * @cursor_size: The size constant of cursor pattern
+ *
+ * The argument given in @cursor_size is one of the CUR_ constants, as stored
+ * in struct @vc_data.vc_cursor_type. For unknown values, the helper draws the
+ * default cursor or an underline dash.
+ *
+ * Returns:
+ * A valid cursor size for the given size value
+ */
+unsigned int vc_cursor_valid_size(unsigned int cursor_size)
+{
+	const unsigned int cursor_default_size = CUR_SIZE(READ_ONCE(cur_default));
+
+	do {
+		switch (cursor_size) {
+		case CUR_NONE:
+		case CUR_UNDERLINE:
+		case CUR_LOWER_THIRD:
+		case CUR_LOWER_HALF:
+		case CUR_TWO_THIRDS:
+		case CUR_BLOCK:
+			return cursor_size;
+		default:
+			pr_warn_once("Unknown cursor %u\n", cursor_size);
+			fallthrough;
+		case CUR_DEF:
+			/*
+			 * Use user-given default size, or underline if
+			 * the given default is invalid.
+			 */
+			if (cursor_size != cursor_default_size)
+				cursor_size = cursor_default_size;
+			else
+				cursor_size = CUR_UNDERLINE;
+		}
+	} while (true);
+}
+EXPORT_SYMBOL_GPL(vc_cursor_valid_size);
+
+/**
+ * vc_cursor_start - Calculates the cursor's first scanline within a character cell
+ * @cell_height: The overall height of the character cell
+ * @cursor_size: The size constant of cursor pattern
+ *
+ * The parameter @cell_height is the height of the character cell as
+ * displayed by the console. The argument given in @cursor_size is one
+ * of the CUR_ constants. See vc_cursor_valid_size() for how to get a
+ * valid cursor-size constant.
+ *
+ * Returns:
+ * The index of the cursor's first scanline within the character cell
+ */
+unsigned int vc_cursor_start(unsigned int cell_height, unsigned int cursor_size)
+{
+	switch (cursor_size) {
+	case CUR_NONE:
+		return cell_height;
+	case CUR_UNDERLINE:
+	default:
+		if (cell_height < 10)
+			return cell_height - 1;
+		else
+			return cell_height - 3;
+	case CUR_LOWER_THIRD:
+		return cell_height - cell_height / 3;
+	case CUR_LOWER_HALF:
+		return cell_height - cell_height / 2;
+	case CUR_TWO_THIRDS:
+		return cell_height - (cell_height * 2) / 3;
+	case CUR_BLOCK:
+		return 0;
+	}
+}
+EXPORT_SYMBOL_GPL(vc_cursor_start);
+
+/**
+ * vc_cursor_end - Calculates the first scanline after the cursor within a character cell
+ * @cell_height: The overall height of the character cell
+ * @cursor_size: The size constant of cursor pattern
+ *
+ * The parameter @cell_height is the height of the character cell as
+ * displayed by the console. The argument given in @cursor_size is one
+ * of the CUR_ constants. See vc_cursor_valid_size() for how to get a
+ * valid cursor-size constant.
+ *
+ * Returns:
+ * The index of the first scanline after the cursor within the character cell
+ */
+unsigned int vc_cursor_end(unsigned int cell_height, unsigned int cursor_size)
+{
+	switch (cursor_size) {
+	case CUR_UNDERLINE:
+	default:
+		if (cell_height < 10)
+			return cell_height;
+		else
+			return cell_height - 1;
+	case CUR_NONE:
+	case CUR_LOWER_THIRD:
+	case CUR_LOWER_HALF:
+	case CUR_TWO_THIRDS:
+	case CUR_BLOCK:
+		return cell_height;
+	}
+}
+EXPORT_SYMBOL_GPL(vc_cursor_end);
+
 /*
  * /sys/class/tty/tty0/
  *

@@ -204,6 +204,10 @@ struct vc {
 extern struct vc vc_cons [MAX_NR_CONSOLES];
 extern void vc_SAK(struct work_struct *work);
 
+/*
+ * Cursors
+ */
+
 #define CUR_MAKE(size, change, set)	((size) | ((change) << 8) |	\
 		((set) << 16))
 #define CUR_SIZE(c)		 ((c) & 0x00000f)

@@ -222,6 +226,10 @@ extern void vc_SAK(struct work_struct *work);
 #define CUR_CHANGE(c)		 ((c) & 0x00ff00)
 #define CUR_SET(c)		(((c) & 0xff0000) >> 8)
 
+unsigned int vc_cursor_valid_size(unsigned int cursor_size);
+unsigned int vc_cursor_start(unsigned int cell_height, unsigned int cursor_size);
+unsigned int vc_cursor_end(unsigned int cell_height, unsigned int cursor_size);
+
 bool con_is_visible(const struct vc_data *vc);
 
 #endif /* _LINUX_CONSOLE_STRUCT_H */