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From: Andrew Morton <akpm@digeo.com>
To: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Jason Howard <lists@spectsoft.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: DMA from SCSI controller to PCI frame buffer memory.
Date: Fri, 13 Dec 2002 21:24:42 -0800	[thread overview]
Message-ID: <3DFAC09A.C5642879@digeo.com> (raw)
In-Reply-To: <1039837312.25121.115.camel@irongate.swansea.linux.org.uk>

Alan Cox wrote:
> 
> On Fri, 2002-12-13 at 19:15, Jason Howard wrote:
> > Hello All,
> >
> > I am wondering if the functionality exists in the Linux kernel to DMA
> > from a SCSI controller directly into frame buffer memory of a PCI video
> > card?  Is there a standard method for this (similar to sendfile) or will
> > it require some hacking?
> 
> 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).

An O_DIRECT disk read into a mmapped device region will fail (if
it doesn't, it'll oops ;)).  O_DIRECT requires valid pages inside
mem_map[].

See the `vma->vm_flags & VM_IO' test in get_user_pages(), and
the VALID_PAGE() test in get_page_map().

Hacking is required to do this.

  reply	other threads:[~2002-12-14  5:17 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2002-12-13 19:15 Jason Howard
2002-12-14  3:41 ` Alan Cox
2002-12-14  5:24   ` Andrew Morton [this message]
2002-12-14 20:29   ` Jason Howard
2002-12-15  2:06 Douglas Gilbert

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