Re: [PATCH 1/1] Userspace I/O (UIO): Add support for userspace DMA(corrected)

From: Greg KH
Date: Wed Dec 03 2008 - 23:47:18 EST

On Wed, Dec 03, 2008 at 05:51:30PM -0800, Edward Estabrook wrote:
> From: Edward Estabrook <Edward_Estabrook@xxxxxxxxxxx>
> Here is a patch that adds the ability to dynamically allocate and use
> coherent DMA
> from userspace by extending the Userspace IO driver. This patch applies against
> 2.6.28-rc6.
> The gist of this implementation is to overload uio's mmap
> functionality to allocate
> and map a new DMA region on demand. The bus-specific DMA address as returned by
> dma_alloc_coherent is made available to userspace in the 1st long word
> of the newly
> created region (as well as through the conventional 'addr' file in sysfs).
> The kernel-api change is that passing an offset value of 0xFFFFF000UL
> to the a uio
> device's mmap operation will dynamically allocate a DMA region. This
> cannot change/
> break existing behavior as the previous UIO code only allowed a maximum of 5
> mappings.

Odd formatting of your paragraphs :(

Anyway, what about 64bit processors? What happens if they try to use a
valid address in this range?

Is this value always an "invalid" value for all arches that Linux runs


greg k-h
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at