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Re: PCI arbiter memory mapping

From: Sergey Bugaev
Subject: Re: PCI arbiter memory mapping
Date: Tue, 17 Aug 2021 00:07:29 +0300

On Mon, Aug 16, 2021 at 11:43 PM Samuel Thibault
<samuel.thibault@gnu.org> wrote:
> Here, possibly proxies can indeed work properly. But please do look at
> what Joan's situation is to make sure it does.

I don't think I understand enough about the situation. It would help
if you or Joan were to kindly give me some more context :)

As I understand it, there's the PCI arbiter, which is a translator
that arbitrates access to PCI, which is a hardware bus that various
devices can be connected to. The hardware devices connected via PCI
are available (to the PCI arbiter) as Mach devices, and in particular
it's possible to use device_map () and then vm_map () to access the
device memory. Then there's libpciaccess whose Hurd backend uses the
files exported by the PCI arbiter to get access to the PCI, including
mapping device memory. Naturally its user can request read-only or
read-write mapping, but the PCI arbiter may decide to only return a
read-only memory object (a proxy to the device pager), in which case
libpciaccess should deallocate the port and return EPREM, or the PCI
arbiter may return the real device pager.

Is that right? What am I missing? What's the issue you're trying to solve?


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