What is SlowBcopy and why is it disabled for the BSDs?

[b-aaz]

This is the file in question.
I don't really get what it does and why it exists.

I had this question after reading this X.Org patch file in the ports tree that enables it for X.Org.
The vesa driver seams to depend on it, so I have enabled it for XLibre too.
But I want to understand it's purpose so that I could see what is exactly happening here.
One thing I know is that sometimes compilers just replace functions like this that just copy bytes with memcpy, so it becomes pointless to use them instead of just memcpy. I think this is what is happening here ... .

[b-aaz]

@metux?

[metux]

I guess it's for old strange platforms where mmio doesn't work as expected but needs extra slowdown. Not sure whether it's still needed today.
Maybe we could make a build time switch and see what happens.

[b-aaz]

The VESA module still needs it (on FreeBSD at least), and complains if it is not present.

[takagemacoed]

I also found this conversation in the commit message. Hope this help.

[SuperDuperDeou]

Do you have any idea about which platforms we're talking about? After a quick search, it looks like to me nobody even knows which hardware requires it. The best I've got is "1995 VGA".

[metux]

it seems, today, it's a workaround for some broken emulators/hypervisors like vbox.