tty: vt: sanitize consw::con_putc() parameters

Make parameters of consw::con_putc() saner:
* x and y are unsigned now, as they cannot be negative, and
* ca is made u16, as it is composed of two 8bit values (character and
  attribute). See the con_putcs() hook, u16/ushort is worked on there.

And document the hook.
Signed-off-by: "Jiri Slaby (SUSE)" <jirislaby@kernel.org>
Cc: Helge Deller <deller@gmx.de>
Cc: linux-fbdev@vger.kernel.org
Cc: dri-devel@lists.freedesktop.org
Tested-by: Helge Deller <deller@gmx.de> # parisc STI console
Link: https://lore.kernel.org/r/20240122110401.7289-26-jirislaby@kernel.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/video/console/dummycon.c

@@ -50,7 +50,8 @@ void dummycon_unregister_output_notifier(struct notifier_block *nb)
 	raw_notifier_chain_unregister(&dummycon_output_nh, nb);
 }
 
-static void dummycon_putc(struct vc_data *vc, int c, int ypos, int xpos)
+static void dummycon_putc(struct vc_data *vc, u16 c, unsigned int y,
+                          unsigned int x)
 {
 	WARN_CONSOLE_UNLOCKED();
 
@@ -84,7 +85,8 @@ static int dummycon_blank(struct vc_data *vc, int blank, int mode_switch)
 	return 1;
 }
 #else
-static void dummycon_putc(struct vc_data *vc, int c, int ypos, int xpos) { }
+static void dummycon_putc(struct vc_data *vc, u16 c, unsigned int y,
+			  unsigned int x) { }
 static void dummycon_putcs(struct vc_data *vc, const unsigned short *s,
 			   int count, int ypos, int xpos) { }
 static int dummycon_blank(struct vc_data *vc, int blank, int mode_switch)

drivers/video/console/newport_con.c

@@ -367,8 +367,8 @@ static void newport_clear(struct vc_data *vc, unsigned int sy, unsigned int sx,
 	}
 }
 
-static void newport_putc(struct vc_data *vc, int charattr, int ypos,
-			 int xpos)
+static void newport_putc(struct vc_data *vc, u16 charattr, unsigned int ypos,
+			 unsigned int xpos)
 {
 	unsigned char *p;
 

include/linux/console.h

@@ -39,6 +39,8 @@ enum vc_intensity;
  * @con_init:   initialize the console on @vc. @init is true for the very first
  *		call on this @vc.
  * @con_clear:  erase @count characters at [@x, @y] on @vc. @count >= 1.
+ * @con_putc:   emit one character with attributes @ca to [@x, @y] on @vc.
+ *		(optional -- @con_putcs would be called instead)
  * @con_scroll: move lines from @top to @bottom in direction @dir by @lines.
  *		Return true if no generic handling should be done.
  *		Invoked by csi_M and printing to the console.
@@ -53,7 +55,8 @@ struct consw {
 	void	(*con_deinit)(struct vc_data *vc);
 	void	(*con_clear)(struct vc_data *vc, unsigned int y,
 			     unsigned int x, unsigned int count);
-	void	(*con_putc)(struct vc_data *vc, int c, int ypos, int xpos);
+	void	(*con_putc)(struct vc_data *vc, u16 ca, unsigned int y,
+			    unsigned int x);
 	void	(*con_putcs)(struct vc_data *vc, const unsigned short *s,
 			int count, int ypos, int xpos);
 	void	(*con_cursor)(struct vc_data *vc, int mode);