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

Chase Douglas chase.douglas at canonical.com
Fri Mar 26 11:51:48 UTC 2010

On Fri, Mar 26, 2010 at 4:12 AM, Amit Kucheria
<amit.kucheria at canonical.com> wrote:
> On 10 Mar 25, Chase Douglas 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).
> So what happens in the case where vga16fb is the first one loaded and some
> other (better) fb is loaded later?

There's two answers:

1. This patch is in vga16fb itself, so it only prevents itself from
registering as a framebuffer. If vga16fb gets /dev/fb0, any other
framebuffer can still register further framebuffers.

2. That doesn't really matter cause we're screwed if vga16fb is first
when we try to use KMS. KMS drivers have their own fb, but only
/dev/fb0 is ever used, so you get bad interactions in that case.
Thankfully, no one seems to be having this issue anymore because the
KMS drivers are loaded before vga16fb and module loading is serialized
by the kernel. If we do find it happens, we may have to tell people to
blacklist vga16fb manually. All this is secondary to the issue fixed
by this patch, however.

-- Chase

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