[Linux-fbdev-devel] fbdev API problems

[Sottek, M. J <mat...@in...>]

I've been working on a sane i810 framebuffer that makes use of the chipset
in the manner
that it was designed to be used. This turns out to be very hard to work into
the existing
2.4.x framebuffer API due to lots of assumptions and generic code not being
very well
suited to my needs.

My basic issues surround the mixing of driver private information (memory
pointers, mmio
regions and other stuff that should NEVER be touched outside the driver)
with information
that gets leaked outside the driver, and even into user space.

On i810 there is a region (512k or 1MB) that is stolen from the top of
memory by the bios
before the OS gains control. This memory is used, via hardware remapping of
0xa0000 and
memory paging, for vga compatibility and for video drivers that do not use
AGP services.
In order to make the framebuffer play nicely with the DRM and X server I am
making a
framebuffer driver that, by default, only uses this stolen memory. The X
server and framebuffer
will then never have problems with ringbuffer corruption, Gart resource
sharing etc.

Now to the problem. I do not have a physical memory region that can be
accessed linearly
for the entire contents of the framebuffer. Not an issue provided that no
one outside the
driver tries to access the memory pointers (I was concerned from the
beginning when I
was asked to provide pointers to data structures that shouldn't have them).
I wrote my
own character functions that are aware of my memory bank switching, and I
have a
mmap function that will use zero page fault handlers to bank switch, map,
and unmap
regions to provide a linear appearance to user space. BUT, it seems that the
logo code,
and possibly some other things still want to touch the video memory. This
can't happen!
I saw reference to an imageblit function in some documents but it may be
from an older
implementation. Clearly that is what I need since I cannot allow anyone
outside my driver
to directly access memory pointers.

Can someone offer some advice as to what I should do to prevent the logo
code and others
from touching my memory pointers.

Second, there is no reason that driver private information should be
provided outside the
driver. Can we make sure that these things go away in the redesign (I
haven't looked though
the new code yet, hopefully such nonsense is gone already)

 -Matt