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

[Javier Martinez Canillas <javierm@redhat.com>]

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/

Best regards,
-- 
Javier Martinez Canillas
Linux Engineering
Red Hat