linux-kernel - Re: [PATCH v2 0/2] PCI: xgene: Restore working PCIe functionnality

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Message-ID: <Yjnfr7V6egc1sewb@robh.at.kernel.org>
Date:   Tue, 22 Mar 2022 09:39:43 -0500
From:   Rob Herring <robh@...nel.org>
To:     Robin Murphy <robin.murphy@....com>, Marc Zyngier <maz@...nel.org>
Cc:     dann frazier <dann.frazier@...onical.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        PCI <linux-pci@...r.kernel.org>,
        Toan Le <toan@...amperecomputing.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Stéphane Graber <stgraber@...ntu.com>,
        Android Kernel Team <kernel-team@...roid.com>
Subject: Re: [PATCH v2 0/2] PCI: xgene: Restore working PCIe functionnality

On Tue, Mar 22, 2022 at 01:16:35PM +0000, Robin Murphy wrote:
> On 2022-03-21 20:06, Robin Murphy wrote:
> > On 2022-03-21 19:21, Marc Zyngier wrote:
> > > On Mon, 21 Mar 2022 18:03:27 +0000,
> > > Rob Herring <robh@...nel.org> wrote:
> > > > 
> > > > On Mon, Mar 21, 2022 at 11:36 AM Marc Zyngier <maz@...nel.org> wrote:
> > > > > 
> > > > > On Mon, 21 Mar 2022 15:17:34 +0000,
> > > > > Rob Herring <robh@...nel.org> wrote:
> > > > > > 
> > > > > > On Mon, Mar 21, 2022 at 5:49 AM Marc Zyngier <maz@...nel.org> wrote:
> > > > > > > 
> > > > > > For XGene-1, I'd still like to understand what the issue is. Reverting
> > > > > > the first fix and fixing 'dma-ranges' should have fixed it. I need a
> > > > > > dump of how the IB registers are initialized in both cases. I'm not
> > > > > > saying changing 'dma-ranges' in the firmware is going to be required
> > > > > > here. There's a couple of other ways we could fix that without a
> > > > > > firmware change, but first I need to understand why it broke.
> > > > > 
> > > > > Reverting 6dce5aa59e0b was enough for me, without changing anything
> > > > > else.
> > > > 
> > > > Meaning c7a75d07827a didn't matter for you. I'm not sure that it would.
> > > > 
> > > > Can you tell me what 'dma-ranges' contains on your system?
> > > 
> > > Each pcie node (all 5 of them) has:
> > > 
> > > dma-ranges = <0x42000000 0x80 0x00 0x80 0x00 0x00 0x80000000
> > >                0x42000000 0x00 0x00 0x00 0x00 0x80 0x00>;

This is the same as what Stéphane has for Merlin. So c7a75d07827a ("PCI: 
xgene: Fix IB window setup") should have fixed Mustang.

> > 
> > Hmm, is there anyone other than iommu-dma who actually depends on the
> > resource list being sorted in ascending order of bus address? I recall
> > at the time I pushed for creating the list in sorted order as it was the
> > simplest and most efficient option, but there's no technical reason we
> > couldn't create it in as-found order and defer the sorting until
> > iova_reserve_pci_windows() (at worst that could even operate on a
> > temporary copy if need be). It's just more code, which didn't need to
> > exist without a good reason, but if this is one then exist it certainly
> > may.
> 
> Taking a closer look, the Cadence driver is already re-sorting the list
> for its own setup, so iommu-dma can't assume the initial sort is
> preserved and needs to do its own anyway. Does the (untested) diff below
> end up helping X-Gene also?

There's no IOMMU on X-Gene 1 or 2 based on the upstream dts files, so 
how would this matter?

Rob