On Thu, 4 Nov 1999, Adam Meyerowitz wrote:
> James,
>
> Yes it is an actually video card and I am using fbcon. In my user space
> process I have no problem mapping the memory and using it via a pointer.
Your doing a mmap of fb_fix_screeninfo.smem_start in userland. Yes this
will work. This pointer you retrieve from mmap in userland only works for
the process that mmapped it. Its the virtual memory address with respect
to the process. Say you have 2 process that mmap the framebuffer. The
physical address (fix.smem_start) will be the same but the pointer
returned from the mmap will be different for each process.
> However in the rtlinux module, I tried mmap (which was successful) and then
> once I accessed the pointer the kernel complained.
Can you post the code so I can look at it. I need to see what exactly you
are trying to do.
> Are you implying that instead of using mmap on /dev/mem in the rtlinux module
> I should be using /dev/fb0 and then do a mmap on that.
Yes. Wait, are you mmapping in the module itself? You don't need to do
that.
> Someone suggested using ioremap in the module but that appears to act on
> io space which is not what I want.
Io space is pci space for machines with a pci bus. You have the normal RAM
that occupies the lower memory regions of a machine. Then you have the pci
bus which maps the memory it has on board a pci card into the high address
of a system. In theory high enough that its doesn't overlap memory in the
lower regions. So ioremap maps the memory in pci space to system memory
space. By the way ioremap works for most buses. I think only sparcs the
rules are different. So yes you need a ioremap in the fbcon module. Now as
for your question on how to access that memory. In fbcon their is a
display struct that is the data structure that interfaces the console
system with framebuffer drivers. In that struct there exist a screen_base
which is the ioremap video memory. If you look in fbcon-cfbX you will see
direct access to the video memory from the kernel. In display their is a
field called screen_base. This is what you want to use to access the
framebuffer from the kernel in your driver. If you look at fbcon-cfb32.c
in function fbcon_cfb32_putc you will see the function places font data
into the framebuffer using screen_base. So what basically is done their is
what you will need to do. If you need help just email me.
> Thanks for the help
> Adam
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