LinuxKPI: Import MTRR support functions from drm-kmod

[wulf]

Summary

They are superseded by PAT and mostly useless nowadays but still can be
used on Pentium III/IV era processors. Unlike drm-kmod version, this one
ignores MTRR if PAT is available that fixes confusing "Failed to add WC
MTRR for [0xXXXX-0xYYYY]: 22; performance may suffer" message often
appearing during drm-kmod initialization process.

MFC after: 1 week

[• hselasky]

sys/compat/linuxkpi/common/include/linux/io.h

491

Add some more ()'s like this to avoid confusion:

(((x) < __MTRR_ID_BASE) ? -1 : ((x) - __MTRR_ID_BASE))

sys/compat/linuxkpi/common/src/linux_page.c

426

I assume there is not race to remove IDR's ?

[wulf]

sys/compat/linuxkpi/common/include/linux/io.h

491

Ok. I will add them

sys/compat/linuxkpi/common/src/linux_page.c

426

I see no race as idr_remove takes idr lock:

void *
idr_remove(struct idr *idr, int id)
{
 	void *res;

	mtx_lock(&idr->lock);
	res = idr_remove_locked(idr, id);
	mtx_unlock(&idr->lock);

	return (res);
}