Re: user_to_phys() without mmap?

phil-news-nospam@xxxxxxxx writes:
On Sun, 15 Jul 2007 00:20:45 +0200 Rainer Weikusat <rweikusat@xxxxxxxxxxx> wrote:
| Neil Steiner <neil.steiner@xxxxxx> writes:
|> I'm trying to use a framebuffer from user space (think plain video
|> ram, not some PCI or AGP video card), but mmap'ing from kernel space
|> into user space is causing large latencies and unsightly artifacts.
|> It appears that anything written into the mmap'ed user memory is in
|> fact being copied into kernel space.
|
| Theoretically, this could probably be implemented with help of the
| MMU and some 'weird' fault handling, but I don't think someone would
| take the trouble, because it seems pretty useless. The /dev/mem driver
| certainly doesn't do this. Only the MMU will interfere accesses to
| virtual memory locations from user space, except for faults caused by
| this accesses.

I tried to map the video buffer into user space some time ago and I did
find that what was mapped was not the actual physical memory of the video
card, but just some memory apparently allocated by a driver in the kernel
which was then periodically copied from that memory into the real physical
memory.

Which driver? That should be easy to determine.
.

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