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

[Sam Ravnborg <sam@ravnborg.org>]

Hi Javier,
On Thu, Feb 24, 2022 at 10:02:59AM +0100, Javier Martinez Canillas wrote:
> Hello Sam,
> 
> On 2/23/22 21:25, Sam Ravnborg wrote:
> 
> [snip]
> 
> > 
> > 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:
> 
>   Documentation/isdn/README.diversion:   (CFB). 
>   drivers/video/pmag-ba-fb.c: *   PMAG-BA TURBOchannel Color Frame Buffer (CFB) card support,
>   include/video/pmag-ba-fb.h: *   TURBOchannel PMAG-BA Color Frame Buffer (CFB) card support,
> 
> 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.
> 
> So the sys_* variants where introduced by commit 68648ed1f58d ("fbdev: add
> drawing functions for framebuffers in system RAM") to fix this. The old
> ones just kept their name, but probably it should had been renamed to io_*
> for the naming to be consistent with the sys_* functions.
> 
> [0]: https://git.kernel.org/pub/scm/linux/kernel/git/history/history.git/

Interesting - thanks for the history lesson and thanks for taking your
time to share your findings too.

	Sam