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

[Chase Douglas]

Version 2 spits out the following at boot:

[   19.806985] vga16fb: initializing
[   19.806989] vga16fb: mapped to 0xffff8800000a0000
[   19.806992] vga16fb: not registering due to another framebuffer present

-- Chase

On Thu, Mar 25, 2010 at 2:59 PM, Chase Douglas
<chase.douglas at canonical.com> wrote:
> 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
>
>
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