linux-kernel - Re: [PATCHv9 00/12] PCI: Recode Mobiveil driver and add PCIe Gen4 driver for NXP Layerscape SoCs

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Date:   Tue, 11 Feb 2020 17:14:41 +0200
From:   Laurentiu Tudor <laurentiu.tudor@....com>
To:     Olof Johansson <olof@...om.net>,
        Robin Murphy <robin.murphy@....com>
Cc:     Li Yang <leoyang.li@....com>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        "arnd@...db.de" <arnd@...db.de>,
        "m.karthikeyan@...iveil.co.in" <m.karthikeyan@...iveil.co.in>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "Z.q. Hou" <zhiqiang.hou@....com>,
        "l.subrahmanya@...iveil.co.in" <l.subrahmanya@...iveil.co.in>,
        "will.deacon@....com" <will.deacon@....com>,
        Russell King - ARM Linux admin <linux@...linux.org.uk>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "M.h. Lian" <minghuan.lian@....com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        Xiaowei Bao <xiaowei.bao@....com>,
        "catalin.marinas@....com" <catalin.marinas@....com>,
        "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
        "andrew.murray@....com" <andrew.murray@....com>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        Mingkai Hu <mingkai.hu@....com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCHv9 00/12] PCI: Recode Mobiveil driver and add PCIe Gen4
 driver for NXP Layerscape SoCs



On 11.02.2020 16:48, Olof Johansson wrote:
> On Tue, Feb 11, 2020 at 5:04 AM Robin Murphy <robin.murphy@....com> wrote:
>>
>> On 2020-02-11 12:13 pm, Laurentiu Tudor wrote:
>> [...]
>>>> This is a known issue about DPAA2 MC bus not working well with SMMU
>>>> based IO mapping.  Adding Laurentiu to the chain who has been looking
>>>> into this issue.
>>>
>>> Yes, I'm closely following the issue. I actually have a workaround
>>> (attached) but haven't submitted as it will probably raise a lot of
>>> eyebrows. In the mean time I'm following some discussions [1][2][3] on
>>> the iommu list which seem to try to tackle what appears to be a similar
>>> issue but with framebuffers. My hope is that we will be able to leverage
>>> whatever turns out.
>>
>> Indeed it's more general than framebuffers - in fact there was a
>> specific requirement from the IORT side to accommodate network/storage
>> controllers with in-memory firmware/configuration data/whatever set up
>> by the bootloader that want to be handed off 'live' to Linux because the
>> overhead of stopping and restarting them is impractical. Thus this DPAA2
>> setup is very much within scope of the desired solution, so please feel
>> free to join in (particularly on the DT parts) :)
> 
> That's a real problem that nees a solution, but that's not what's
> happening here, since cold boots works fine.
> 
> Isn't it a whole lot more likely that something isn't
> reset/reinitialized properly in u-boot, such that there is lingering
> state in the setup, causing this?

Ok, so this is completely something else. I don't think our u-boots are 
designed to run in ways other than coming from hard reset.

>> As for right now, note that your patch would only be a partial
>> mitigation to slightly reduce the fault window but not remove it
>> entirely. To be robust the SMMU driver *has* to know about live streams
>> before the first arm_smmu_reset() - hence the need for generic firmware
>> bindings - so doing anything from the MC driver is already too late (and
>> indeed the current iommu_request_dm_for_dev() mechanism is itself a
>> microcosm of the same problem).
> 
> This is more likely a live stream that's left behind from the previous
> kernel (there are some error messages about being unable to detach
> domains, but the errors make it hard to tell what driver didn't unbind
> enough).

I also noticed those messages. Perhaps our PCI driver doesn't do all the 
required cleanup.

> *BUT*, even with that bug, the system should reboot reliably and come
> up clean. So, something isn't clearing up the state *on boot*.

We do test some kexec based "soft-reset" scenarios, didn't hit your 
issue but instead we hit this:

https://lkml.org/lkml/2018/9/21/1066

Can you please provide some more info on your scenario?

---
Best Regards, Laurentiu