linux-kernel - Re: Providing access to kernel memory from PCI bus

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Message-ID: <48769EE4.3050101@shaw.ca>
Date:	Thu, 10 Jul 2008 17:44:36 -0600
From:	Robert Hancock <hancockr@...w.ca>
To:	darrell.holigan@...il.com
CC:	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: Providing access to kernel memory from PCI bus

darrell.holigan@...il.com wrote:
> I'm developing a PCI driver under linux to communicate with an Intel
> IQ80331 which supports PCI boot.  To accomplish this, the IQ80331
> needs access to an image stored in the host processor's (AMCC 405GPr)
> RAM.
> 
> Linux boots, sees the PCI bridge and the address translation unit on
> the IQ80331 (core is held in reset) and calls the probe function my
> driver which retrieves the address allocated to BAR0 and ioremaps it.
> The IQ80331 implements a single BAR which provides access to ATU
> registers.
> 
> From here, I can configure the IQ80331 through BAR0 to do a long jump
> at boot.  According to the dev manual I need to configure the outbound
> window of the ATU so that it translates the jump to host memory where
> my boot image is stored.
> 
> I have kmalloced kernel memory in my driver's ioctl and loaded in the
> image from user space, but I do not understand the process to tell the
> kernel that I want the kmalloced area available for access from PCI
> devices.  I assume that I must do this explicitly since allowing
> unrestricted access to kernel memory from PCI space would be a
> security/stabilty concern, yes?  But I cannot find the proper kernel
> API calls to do this.

You should likely allocate the memory that you are making available to 
the device using dma_alloc_coherent. That will give you a bus address 
that points to the memory that you can give to your device.
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