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

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Date:   Mon, 21 Mar 2022 20:06:40 +0000
From:   Robin Murphy <robin.murphy@....com>
To:     Marc Zyngier <maz@...nel.org>, Rob Herring <robh@...nel.org>
Cc:     "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>,
        dann frazier <dann.frazier@...onical.com>,
        Android Kernel Team <kernel-team@...roid.com>
Subject: Re: [PATCH v2 0/2] PCI: xgene: Restore working PCIe functionnality

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>;

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.

Cheers,
Robin.