Hmm interesting... when you say mmaped video memory, do you mean PCI/AGP
memory *on* the video card, or system RAM? I believe some of the replies
indicating that it should work were talking about system RAM?
I think the normal case is DMA from scsi card or ide or whatever to/from
system RAM. I don't think (but I don't know that much) that DMA from a scsi
card to another PCI card is the normal case. Can anyone comment furthur?
Jeremy
----- Original Message -----
From: "Rick Smith" <rgsmith72@xxxxxxxxxxx>
To: <linux-xfs@xxxxxxxxxxx>
Sent: Thursday, May 08, 2003 6:16 PM
Subject: O_DIRECT address restrictions
> Hello,
> What are the memory address restrictions when using the O_DIRECT flag
> with XFS? I am trying to perform I/O directly from the filesystem to a
piece
> of mmap'ed video memory and I get the "bad address" error when I attempt
to
> do so with O_DIRECT. Without the O_DIRECT flag I am able to perform the
I/O
> but is it must too slow. Using O_DIRECT with other system memory seems to
> work fine, but I would like the option of transferring data directly to a
> video card without a bounce buffer and a DMA step. Is direct I/O available
> to any memory address that satisfies the alignment requirement or must
this
> address be below the MAX_DMA_ADDR?
>
> Any help appreciated. Thanks.
>
> Rick Smith
>
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