Re: [PATCH v3 4/5] fbdev: Improve performance of cfb_imageblit()

[Geert Uytterhoeven <geert@linux-m68k.org>]

Hi Javier,

On Thu, Feb 24, 2022 at 10:03 AM Javier Martinez Canillas
<javierm@redhat.com> wrote:
> On 2/23/22 21:25, Sam Ravnborg wrote:
> > Question: What is cfb an abbreviation for anyway?
> > Not related to the patch - but if I have known the memory is lost..
>
> I was curious so I dug on this. It seems CFB stands for Color Frame Buffer.
> Doing a `git grep "(CFB)"` in the linux history repo [0], I get this:

The naming actually comes from X11.
"mfb" is a monochrome frame buffer (bpp = 1).
"cfb" is a color frame buffer (bpp > 1), which uses a chunky format.

> Probably the helpers are called like this because they were for any fbdev
> driver but assumed that the framebuffer was always in I/O memory. Later some
> drivers were allocating the framebuffer in system memory and still using the
> helpers, that were using I/O memory accessors and it's ilegal on some arches.

Yep.  Graphics memory used to be on a graphics card.
On systems (usually non-x86) where it was part of main memory, usually
it didn't matter at all whether you used I/O memory or plain memory
accessors anyway.

Then x86 got unified memory...

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