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

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Date:	Wed, 3 Dec 2008 20:17:39 -0800
From:	Greg KH <gregkh@...e.de>
To:	Edward Estabrook <edward.estabrook.lkml@...il.com>
Cc:	linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
	hjk@...utronix.de, edward.estabrook@...il.com,
	edward_estabrook@...lent.com
Subject: Re: [PATCH 1/1] Userspace I/O (UIO): Add support for userspace DMA
	(corrected)

On Wed, Dec 03, 2008 at 05:51:30PM -0800, Edward Estabrook wrote:
> From: Edward Estabrook <Edward_Estabrook@...lent.com>
> 
> 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
on?

thanks,

greg k-h
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