linux-kernel - Re: [PATCH V5 2/3] ARM64 LPC: Add missing range exception for special ISA

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Message-ID: <20161109111959.GB17020@leverpostej>
Date:   Wed, 9 Nov 2016 11:20:00 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc:     "zhichang.yuan" <yuanzhichang@...ilicon.com>,
        catalin.marinas@....com, will.deacon@....com, robh+dt@...nel.org,
        bhelgaas@...gle.com, olof@...om.net, arnd@...db.de,
        linux-arm-kernel@...ts.infradead.org, lorenzo.pieralisi@....com,
        linux-kernel@...r.kernel.org, linuxarm@...wei.com,
        devicetree@...r.kernel.org, linux-pci@...r.kernel.org,
        linux-serial@...r.kernel.org, minyard@....org, liviu.dudau@....com,
        zourongrong@...il.com, john.garry@...wei.com,
        gabriele.paoloni@...wei.com, zhichang.yuan02@...il.com,
        kantyzc@....com, xuwei5@...ilicon.com, marc.zyngier@....com
Subject: Re: [PATCH V5 2/3] ARM64 LPC: Add missing range exception for
 special ISA

On Wed, Nov 09, 2016 at 10:12:59AM +1100, Benjamin Herrenschmidt wrote:
> On Tue, 2016-11-08 at 11:49 +0000, Mark Rutland wrote:
> > I believe that we could theoretically have multiple independent LPC/ISA
> > busses, as is possible with PCI on !x86 systems. If the current ISA code
> > assumes a singleton bus, I think that's something that needs to be fixed
> > up more generically.
> > 
> > I don't see why we should need any architecture-specific code here. Why
> > can we not fix up the ISA bus code in drivers/of/address.c such that it
> > handles multiple ISA bus instances, and translates all sub-device
> > addresses relative to the specific bus instance?
> 
> What in that code prevents that today ?

It appears I was mistaken w.r.t. the singleton comment. We can already
translate MMIO->MMIO addresses per-instance (in the presence of a ranges
property).

The big change would be to handle !MMIO translations, for which we'd
need a runtime registry of ISA bus instance to find the relevant
accessor ops and instance-specific data.

Thanks,
Mark.