Re: Advice sought on approach.

[Alex Bennee <kernel-hacker@bennee.com>]

On Wed, 2003-03-05 at 13:26, Antonino Daplas wrote:
> On Wed, 2003-03-05 at 20:37, Alex Bennee wrote:
> > Having read the fb-dev docs on www.linux-fbdev.org I'm a little confused
> > as to what actually puts data into the framebuffer. Most of the
> > framebuffer drivers just seem to deal with resolution and colourmap
> > settings. Is this a case of having to re-implement the fbcon drivers as
> > well to get what I want?
> The pixels placed to the framebuffer are all done in the fbcon-cfb*.c
> modules (if you use the generic functions).  This is for standard
> character drawing.  The logo is drawn indepently (fbcon_show_logo in
> fbcon.c).  User applications write directly to the framebuffer via the
> mmap() function.

I think I understand now. When the fb_set_disp function is called I fill
in the display struction with the console display operations. I've got
two choices now:

1. Create a new fbcon_cfb16 file which notes the changed areas before
calling the generic function.

2. Patch the current fbcon_cfb16 (with a CONFIG option) to add the
change tracking facility in a more generic way.

I guess the question is is it worth doing 2 as a potential upstream
patch? Or is this sort of thing so specialised I should just keep it all
packed in my own fb driver?

I guess I can't easily implement user access via mmap without uploading
the entire screen, which I'm not intending to do anyway because all I
really need is the console support - at least for now.

> > Are there any examples of drivers that have a similar architecture that
> > would be worth looking at? I've had a look at the vfb.c code but again
> > that seems too simplistic compared to what I'll need.
> 
> Search the archives for SED1335.  The author implemented a shadowed
> virtual framebuffer using system memory.  The contents of the virtual
> framebuffer are written to the data port periodically via a timer
> function.

I couldn't find anything in the mail archives but after some careful
googling I found this site (posted for reference):
ftp://ssv-embedded.de/ssv/products/trm916/sample/x86/linux/fbdev which
seems to be the one your refering to.

Thanks for the pointer, seeing the code made things a lot clearer :-)

-- 
Alex, homepage: http://www.bennee.com/~alex/

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	(2) Gardens are for plants to live in.
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