Re: [PATCH] x86: Split off mem*io functions

H. Peter Anvin
2011-12-13T23:47:18Z

On 12/13/2011 02:58 PM, Linus Torvalds wrote:
>
> - some devices (for example, traditional CGA/VGA) read and write to
> different banks and bit modes, so a "read-mask-write" operation just
> does not work at all. You have to do pure writes when copying to such
> a destination. Afaik, none of our *current* memory copies do this for
> partial words, but it's an example of something that is valid (and
> sometimes done) in memcpy to avoid unaligned stores, for example.
>

VGA is even weirder: in some modes (which noone in their sane mind use)
you can make it do operations versus an internal buffer. The catch is
that the internal buffer is only 8 bits wide, so anything other than
byte writes will fail in the extreme in those modes.

-hpa