Framebuffer using system memory

Framebuffer using system memory

[Alessio Sangalli]

Hi I am working on a framebuffer that uses the system memory.

What I mean here is that I need to pass mem=120M to a system that has
128MB to "reserve" 8MB of memory for the framebuffer; then I program the
hardware to use that region of memory.

The reason I do this is that it seems impossible to kmalloc more that
4MB of contiguos physical memory with the Linux Kernel.

Bottom line, I do not know how to map those 8MB back to userspace. If
userspace opens mmaps /dev/mem and writes to the appropriate location it
can access the fb perfectly.

Any hints? All of this is on ARM9.

Thank you
Alessio


------------------------------------------------------------------------------
Crystal Reports - New Free Runtime and 30 Day Trial
Check out the new simplified licensign option that enables unlimited
royalty-free distribution of the report engine for externally facing 
server and web deployment.
http://p.sf.net/sfu/businessobjects

Re: Framebuffer using system memory

[Geert Uytterhoeven]

On Sat, Apr 25, 2009 at 03:13, Alessio Sangalli <alesan@manoweb.com> wrote:
> Hi I am working on a framebuffer that uses the system memory.
>
> What I mean here is that I need to pass mem=120M to a system that has
> 128MB to "reserve" 8MB of memory for the framebuffer; then I program the
> hardware to use that region of memory.
>
> The reason I do this is that it seems impossible to kmalloc more that
> 4MB of contiguos physical memory with the Linux Kernel.
>
> Bottom line, I do not know how to map those 8MB back to userspace. If
> userspace opens mmaps /dev/mem and writes to the appropriate location it
> can access the fb perfectly.
>
> Any hints? All of this is on ARM9.

Alternatively, you could use__alloc_bootmem() in the early platform
code to reserve
the memory, cfr. arch/powerpc/platforms/ps3/setup.c

Gr{oetje,eeting}s,

						Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
							    -- Linus Torvalds

------------------------------------------------------------------------------
Crystal Reports &#45; New Free Runtime and 30 Day Trial
Check out the new simplified licensign option that enables unlimited
royalty&#45;free distribution of the report engine for externally facing 
server and web deployment.
http://p.sf.net/sfu/businessobjects

Re: Framebuffer using system memory

[Alessio Sangalli]

Geert Uytterhoeven wrote:

> Alternatively, you could use__alloc_bootmem() in the early platform
> code to reserve
> the memory, cfr. arch/powerpc/platforms/ps3/setup.c


Yeah thanks, that example is pretty complete. I will try that. Anyway,
for my personal curiosity, is it possible at all to map memory not
managed by the kernel to userspace?

bye
as


------------------------------------------------------------------------------
Crystal Reports - New Free Runtime and 30 Day Trial
Check out the new simplified licensign option that enables unlimited
royalty-free distribution of the report engine for externally facing 
server and web deployment.
http://p.sf.net/sfu/businessobjects

Re: Framebuffer using system memory

[Alessio Sangalli]

Geert Uytterhoeven wrote:

> Alternatively, you could use__alloc_bootmem() in the early platform
> code to reserve
> the memory, cfr. arch/powerpc/platforms/ps3/setup.c


So the usage patter seems to be:

- I use __alloc_bootmem() to reserve memory
- I export a structure that contains data about this memory (location
and size mainly)
- In the init of my framebuffer driver I use the data in that structure
to configure the hardware
- I map that area of memory to userspace when they try to mmap() this fb
device

Can you comment on this?

bye
Alessio


------------------------------------------------------------------------------
Crystal Reports - New Free Runtime and 30 Day Trial
Check out the new simplified licensign option that enables unlimited
royalty-free distribution of the report engine for externally facing 
server and web deployment.
http://p.sf.net/sfu/businessobjects

Re: Framebuffer using system memory

[Geert Uytterhoeven]

On Sat, Apr 25, 2009 at 21:08, Alessio Sangalli <alesan@manoweb.com> wrote:
> Geert Uytterhoeven wrote:
>
>> Alternatively, you could use__alloc_bootmem() in the early platform
>> code to reserve
>> the memory, cfr. arch/powerpc/platforms/ps3/setup.c
>
>
> So the usage patter seems to be:
>
> - I use __alloc_bootmem() to reserve memory
> - I export a structure that contains data about this memory (location
> and size mainly)
> - In the init of my framebuffer driver I use the data in that structure
> to configure the hardware
> - I map that area of memory to userspace when they try to mmap() this fb
> device
>
> Can you comment on this?

That's correct. Note that you don't have to do anything special for mmap()
(i.e. you do not need your own device-specific fb_mmap()), as the default one
should work fine.

If you use a platform device, you can store the memory location and size in the
platform device's platform data.

Gr{oetje,eeting}s,

						Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
							    -- Linus Torvalds

------------------------------------------------------------------------------
Crystal Reports &#45; New Free Runtime and 30 Day Trial
Check out the new simplified licensign option that enables unlimited
royalty&#45;free distribution of the report engine for externally facing 
server and web deployment.
http://p.sf.net/sfu/businessobjects