fbdev: fbcon: check if mode can handle new screen

Check if the mode can properly display the screen.  This will be needed by
drivers where the capability is not constant with each mode.  The function
fb_set_var() will query fbcon the requirement, then it will query the driver
(via a new hook fb_get_caps()) its capability.  If the driver's capability
cannot handle fbcon's requirement, then fb_set_var() will fail.

For example, if a particular driver supports 2 modes where:

mode1 = can only display 8x16 bitmaps
mode2 = can display any bitmap

then if current mode = mode2 and current font = 12x22

fbset <mode1> /* mode1 cannot handle 12x22 */
fbset will fail

Signed-off-by: Antonino Daplas <adaplas@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/video/console/fbcon.c

@@ -3043,13 +3043,51 @@ static void fbcon_new_modelist(struct fb_info *info)
 	}
 }
 
+static void fbcon_get_requirement(struct fb_info *info,
+				  struct fb_blit_caps *caps)
+{
+	struct vc_data *vc;
+	struct display *p;
+	int charcnt;
+
+	if (caps->flags) {
+		int i;
+
+		for (i = first_fb_vc; i <= last_fb_vc; i++) {
+			vc = vc_cons[i].d;
+			if (vc && vc->vc_mode == KD_TEXT) {
+				p = &fb_display[i];
+				caps->x |= 1 << (vc->vc_font.width - 1);
+				caps->y |= 1 << (vc->vc_font.height - 1);
+				charcnt = (p->userfont) ?
+					FNTCHARCNT(p->fontdata) : 256;
+				if (caps->len < charcnt)
+					caps->len = charcnt;
+			}
+		}
+	} else {
+		vc = vc_cons[fg_console].d;
+
+		if (vc && vc->vc_mode == KD_TEXT) {
+			p = &fb_display[fg_console];
+			caps->x |= 1 << (vc->vc_font.width - 1);
+			caps->y |= 1 << (vc->vc_font.height - 1);
+			charcnt = (p->userfont) ?
+				FNTCHARCNT(p->fontdata) : 256;
+			if (caps->len < charcnt)
+				caps->len = charcnt;
+		}
+	}
+}
+
 static int fbcon_event_notify(struct notifier_block *self, 
 			      unsigned long action, void *data)
 {
 	struct fb_event *event = data;
 	struct fb_info *info = event->info;
 	struct fb_videomode *mode;
 	struct fb_con2fbmap *con2fb;
+	struct fb_blit_caps *caps;
 	int ret = 0;
 
 	/*
@@ -3098,6 +3136,10 @@ static int fbcon_event_notify(struct notifier_block *self,
 	case FB_EVENT_NEW_MODELIST:
 		fbcon_new_modelist(info);
 		break;
+	case FB_EVENT_GET_REQ:
+		caps = event->data;
+		fbcon_get_requirement(info, caps);
+		break;
 	}
 
 done:

drivers/video/fbmem.c

@@ -773,6 +773,29 @@ fb_pan_display(struct fb_info *info, struct fb_var_screeninfo *var)
         return 0;
 }
 
+static int fb_check_caps(struct fb_info *info, struct fb_var_screeninfo *var,
+			 u32 activate)
+{
+	struct fb_event event;
+	struct fb_blit_caps caps, fbcaps;
+	int err = 0;
+
+	memset(&caps, 0, sizeof(caps));
+	memset(&fbcaps, 0, sizeof(fbcaps));
+	caps.flags = (activate & FB_ACTIVATE_ALL) ? 1 : 0;
+	event.info = info;
+	event.data = ∩︀
+	fb_notifier_call_chain(FB_EVENT_GET_REQ, &event);
+	info->fbops->fb_get_caps(info, &fbcaps, var);
+
+	if (((fbcaps.x ^ caps.x) & caps.x) ||
+	    ((fbcaps.y ^ caps.y) & caps.y) ||
+	    (fbcaps.len < caps.len))
+		err = -EINVAL;
+
+	return err;
+}
+
 int
 fb_set_var(struct fb_info *info, struct fb_var_screeninfo *var)
 {
@@ -817,7 +840,15 @@ fb_set_var(struct fb_info *info, struct fb_var_screeninfo *var)
 			struct fb_videomode mode;
 			int err = 0;
 
+			if (info->fbops->fb_get_caps) {
+				err = fb_check_caps(info, var, activate);
+
+				if (err)
+					goto done;
+			}
+
 			info->var = *var;
+
 			if (info->fbops->fb_set_par)
 				info->fbops->fb_set_par(info);
 
@@ -843,6 +874,8 @@ fb_set_var(struct fb_info *info, struct fb_var_screeninfo *var)
 			}
 		}
 	}
+
+ done:
 	return 0;
 }
 

include/linux/fb.h

@@ -527,12 +527,20 @@ struct fb_cursor_user {
 #define FB_EVENT_MODE_CHANGE_ALL	0x0B
 /*	A software display blank change occured */
 #define FB_EVENT_CONBLANK               0x0C
+/*      Get drawing requirements        */
+#define FB_EVENT_GET_REQ                0x0D
 
 struct fb_event {
 	struct fb_info *info;
 	void *data;
 };
 
+struct fb_blit_caps {
+	u32 x;
+	u32 y;
+	u32 len;
+	u32 flags;
+};
 
 extern int fb_register_client(struct notifier_block *nb);
 extern int fb_unregister_client(struct notifier_block *nb);
@@ -652,6 +660,10 @@ struct fb_ops {
 
 	/* restore saved state */
 	void (*fb_restore_state)(struct fb_info *info);
+
+	/* get capability given var */
+	void (*fb_get_caps)(struct fb_info *info, struct fb_blit_caps *caps,
+			    struct fb_var_screeninfo *var);
 };
 
 #ifdef CONFIG_FB_TILEBLITTING