* David Herrmann [off-list ref] wrote:

Hi

On Wed, Dec 18, 2013 at 8:42 AM, Takashi Iwai [off-list ref] wrote:

quoted

Hi,

with the recent enablement of simplefb on x86, cirrusdrmfb on QEMU/KVM
gets broken now, as reported at:
    https://bugzilla.novell.com/show_bug.cgi?id…5821

The cirrus VGA resource is reserved at first as "BOOTFB" in
arch/x86/kernel/sysfb_simplefb.c, which is taken by simplefb platform
device.  This resource is, however, never released until the platform
device is destroyed, and the framebuffer switching doesn't trigger
it.  It calls fb's destroy callback, at most.  Then, cirrus driver
tries to assign the resource, fails and gives up, resulting in a
complete blank screen.

The same problem should exist on other KMS drivers like mgag200 or
ast, not only cirrus.  Intel graphics doesn't hit this problem just
because the reserved iomem by BOOTFB isn't required by i915 driver.

The patch below is a quick attempt to solve the issue.  It adds a new
API function for releasing resources of platform_device, and call it
in destroy op of simplefb.  But, forcibly releasing resources of a
parent device doesn't sound like a correct design.  We may take such
as a band aid, but definitely need a more fundamental fix.

Any thoughts?

That bug always existed, simplefb is just the first driver to hit it 
(vesafb/efifb didn't use resources). I'm aware of the issue but as a 
workaround you can simply disable CONFIG_X86_SYSFB. That restores 
the old behavior.

This looks like a regression, so we'll either need a fix or we'll have 
to mark CONFIG_X86_SYSFB as CONFIG_BROKEN.

As a proper fix, I'd propose something like:
  dev = platform_find_device("platform-framebuffer");
  platform_remove_device(dev);

And we wrap this as:
  sysfb_remove_framebuffers()
in arch/x86/kernel/sysfb.c

This should cause a ->remove() event for the platform-driver and
correctly release the resources. Comments?
I will try to write a patch and send it later.

A fix would be awesome.

Thanks,

	Ingo