From mboxrd@z Thu Jan  1 00:00:00 1970
From: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Subject: Re: Frame buffer mmap not working in pvops dom0
Date: Wed, 21 Jul 2010 15:00:56 -0400
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> I have been dumping the page tables (using the attached pt-dump script,
> as qemu's "info tlb" only works on i386) from a paused qemu instance
> that is running a simple mmap-and-spin program (also attached). All 100
> pages map to physical memory address 39a4c000.

The qemu output then isn't going to a VNC window but something else. I
presume the something else is the SDL piece? Were there any special flags
to enable this on QEMU?
> 
> >From a bit more debugging, I've been able to trace the correct address
> (0xf0000000) being lost when it is passed by xen_make_pte to
> pte_pfn_to_mfn and eventually to get_phys_to_machine(0xf0000) which
> returns -1. Still not sure where the final physical address is coming
> from, but I'm guessing this is part of the problem.

That looks like the VM_IO flag (_PAGE_IOMAP on the PTE) is not set somewhere.
Do you have an idea what piece of kernel code gets triggered when QEMU does
'mmap' on the /dev/fb0?

On my machine where I use KMS/DRM it ends up calling 'ttm_fb_mmap'. But
for your system, where it looks that you are using the "old" framebuffer
code it might be something entirely different.

.. snip..
> The attached program has no visible effect on the screen when run, so
> it's likely also not working here.

<nods> Looks quite similar to what I've been using.