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Date:   Mon, 19 Feb 2018 10:30:25 -0500 (EST)
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Subject: Re: [PATCH] sparc: Use generic pci_mmap_resource_range()
From:   David Miller <davem@davemloft.net>
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From: David Woodhouse <dwmw2@infradead.org>
Date: Mon, 19 Feb 2018 15:24:18 +0000

>> For one, the sparc specific code allows mmap'ing any address range
>> within a PCI bus device.??The generic code does not allow that.
> 
> 
> You mean any address range in a given PCI bus even if there is no
> actual device with a BAR at the corresponding address?
> 
> Would I be right to assume this was only available through the legacy
> procfs API? I think it should be possible to accommodate it, and it
> does look like I'd missed this requirement the first time round; thanks
> for pointing it out.

It was probably the case that only procfs could do it.

It is the mechanism by which we were able to let the X server poke
around in VGA ISA space.  It does a bus I/O space map for the bus
device above the VGA card.