From: Tom Smyth <tom.smyth@wirelessconnect.eu>
Subject: Re: 32 bit PCI device DMA - low memory or IOMMU?
To: Geoff Steckel <gwes@oat.com>
Cc: tech <tech@openbsd.org>
Date: Tue, 15 Jul 2025 09:10:46 +0100

Iommu only works with pci-e not a 32 bit pci bus
As far as i know


On Tue, 15 Jul 2025 at 04:45, Geoff Steckel <gwes@oat.com> wrote:
>
> Hi,
>
> I hope this is a simple question.
> If the answer is "maybe" or "there are gotchas" I'll experiment.
>
> I have a 2000-era PCI frame grabber (itifg).
> It can only address 32 bits. It needs huge contiguous buffers.
> Other than that, porting the ancient Linux driver is pretty straightforward.
>
> Given a modern amd64 architecture and 16G,
> is it likely that 100M under 4G would be available at attach time?
> There are no other devices needing low memory.
>
> If not it's IOMMU time and that doesn't look simple.
>
> thanks very much,
> Geoff Steckel
>
>


-- 
Kindest regards,
Tom Smyth.