[PATCH v2] UBUNTU: SAUCE: Don't register vga16fb framebuffer if other framebuffers are present

[Chase Douglas]

Using the vga16fb framebuffer is not safe when other framebuffers are
present. This fixes the case where the vga16fb module is loaded after
a better framebuffer is loaded (since vga16fb is by definition the
worst-case framebuffer).

There does not appear to be any locking around the num_registered_fb, so
this is a hack at best. However, in Lucid we build vga16fb as a module.
Modules are loaded serially, so this should be ok for Lucid. In M, we
will transition to efifb and drop vga16fb, so this is a one time hack.

This prevents sudo lshw from corrupting /dev/fb0 by writing to vga16fb
through /dev/fb1.

BugLink: http://bugs.launchpad.net/bugs/527369

Signed-off-by: Chase Douglas <chase.douglas at canonical.com>
---
 drivers/video/vga16fb.c |   10 ++++++++++
 1 files changed, 10 insertions(+), 0 deletions(-)

diff --git a/drivers/video/vga16fb.c b/drivers/video/vga16fb.c
index efde41d..d8f8313 100644
--- a/drivers/video/vga16fb.c
+++ b/drivers/video/vga16fb.c
@@ -1355,6 +1355,16 @@ static int __init vga16fb_probe(struct platform_device *dev)
 
 	vga16fb_update_fix(info);
 
+	/*
+	 * Ubuntu: Don't register vga16fb if another fb exists. Bad interactions
+	 * can occur.
+	 */
+	if (num_registered_fb > 0) {
+		printk(KERN_NOTICE "vga16fb: not registering due to another "
+		       "framebuffer present\n");
+		goto err_check_var;
+	}
+
 	if (register_framebuffer(info) < 0) {
 		printk(KERN_ERR "vga16fb: unable to register framebuffer\n");
 		ret = -EINVAL;
-- 
1.7.0