Re: user_to_phys() without mmap?

On Mon, 16 Jul 2007 14:46:24 +0200 Rainer Weikusat <rweikusat@xxxxxxxxxxx> wrote:
| 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.

The basic console driver used for text and framebuffer modes. Those are
standard common modes across all video cards that support legacy VGA, so
there is just one driver. I don't know that it has a particular name.

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