Re: DMA from SCSI controller to PCI frame buffer memory.

From: Jason Howard (
Date: Sat Dec 14 2002 - 15:29:54 EST

> In theory you can mmap the frame buffer memory, then do O_DIRECT I/O
> into it. In practice it will buffer (I hope it still does). One of the
> problems is that there are huge lists of PCI->AGP DMA errata in
> chipsets.

I am not accessing the AGP bus as my frame buffer is located on the PCI
00:08.0 Multimedia video controller: Unknown device f1d0:efac
        Subsystem: Unknown device f1d0:efac
        Flags: bus master, stepping, medium devsel, latency 64, IRQ 10
        Memory at f4000000 (32-bit, non-prefetchable) [size=4K]
        Memory at f6000000 (32-bit, prefetchable) [size=16M]
(I am working with the second memory address)

Any recommendations on where to start hacking? Would it be a good idea
to add O_DIRECT to a mmaped PCI space? The kernel should not be doing
any buffering whatsoever, as we will be coming close to filling the pci
bus up with transfers from direct disk->fb already. (We are already
doing buffering on the FB card as well)


 Jason Howard

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