managed pages, into KVA space. Since the pages are managed, we should
use pmap_enter(), not pmap_kenter_pa().
Also, when entering the mappings, enter with an access_type of
VM_PROT_READ | VM_PROT_WRITE. We do this for a couple of reasons:
(1) On systems that have H/W mod/ref attributes, the hardware
may not be able to track mod/ref done by a bus master.
(2) On systems that have to do mod/ref emulation, this prevents
a mod/ref page fault from potentially happening while in an
interrupt context, which can be problematic.
This latter change is fairly important if we ever want to be able to
transfer DMA-safe memory pages to anonymous memory objects; we will need
to know that the pages are modified, or else data could be lost!
Note that while the pages are unowned (i.e. "just DMA-safe memory pages"),
they won't consume any swap resources, as the mappings are wired, and
the pages aren't on the active or inactive queues.
* Map the message buffer with access_type = VM_PROT_READ|VM_PROT_WRITE `just
because'.
* Map the file system buffers with access_type = VM_PROT_READ|VM_PROT_WRITE to
avoid possible problems with pagemove().
* Do not use VM_PROT_EXEC with either of the above.
* Map pages for /dev/mem with access_type = prot. Also, DO NOT use
pmap_kenter() for this, as we DO NOT want to lose modification information.
* Map pages in dumpsys() with VM_PROT_READ.
* Map pages in m68k mappedcopyin()/mappedcopyout() and writeback() with
access_type = prot.
* For now, bus_dma*(), pmap_map(), vmapbuf(), and similar functions still use
access_type = 0. This should probably be revisited.
member to the DMA tag, and calling the direct-mapped back-ends directly,
rather than through chipset-specific front-ends which pass the window
base as an additional argument.
annoyance on systems that prefetch the next page during memory -> device
DMA if the DMA comes within a certain distance of the end of the current
page. This could cause machine checks since the PTE after the last page
would not have the valid bit set.
(I'm not going to complain about this slight kludge too much, since prefetch
makes DMA much faster...)
a function) which specifies how many lines will be skipped when scrolling
up when the bottom of the screen is reached. Dumb framebuffers skip 10
lines (as before) because the copies are s ... l ... o ... w, but it's
silly to skip 10 lines on VGA, since the copies are much faster, so we
only skip one in that case.