Calling PCI Autoconfig again

Mark Chambers markc at
Wed Mar 8 04:22:07 EST 2006

> On Mar 7, 2006, at 10:53 AM, Mark Chambers wrote:
>>> I'm dealing with this exact same situation and having a discussion  
>>> on  lkml regarding the proper way to do this.  In your case, do  
>>> you care  what addresses the FPGA is assigned at?
>> Why does the PCI device have to have a fixed address?   And how do
>> you load an FPGA from user space - mmap?
> In my case it does because we have other devices (DSPs) that are hard  
> coded to know where in PCI address space the FPGA is.

Ah, ok.  So I'm guessing we're talking about DSP bus-master operations
where the DSP is putting out physical PCI space addresses that the
MMU can't help map.  I've run into a similar problem where I'd like to
be able to have a DSP do CPM/BD-like operations from SDRAM, but
it's exceedingly difficult to get the physical address of user-space data.

Well, FWIW, seems to me that something like what Greg K-H referred to,
where you pre-reserve space in PCI land, and then put the device there
when it becomes available, is the way to go.  Otherwise you have this
un-managed hole in PCI space allocation that might cause other problems 
with true hot-swap PCI, or break with kernel revisions.


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