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

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Message-ID: <27e0acfc-0782-bd97-a80e-1143f1315891@nxp.com>
Date:   Tue, 11 Feb 2020 15:55:20 +0200
From:   Laurentiu Tudor <laurentiu.tudor@....com>
To:     Robin Murphy <robin.murphy@....com>, Li Yang <leoyang.li@....com>,
        Olof Johansson <olof@...om.net>
Cc:     "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>,
        Diana Madalina Craciun <diana.craciun@....com>
Subject: Re: [PATCHv9 00/12] PCI: Recode Mobiveil driver and add PCIe Gen4
 driver for NXP Layerscape SoCs



On 11.02.2020 15:04, Robin Murphy 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) :)

Will sure do. Seems that the 2nd approach (the one with list of 
compatibles in arm-smmu) fits really well with our scenario. Will this 
be the way to go forward?

> 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).

I think you might have missed in the patch that it pauses the firmware 
at early boot, in its driver init and it resumes it only after 
iommu_request_dm_for_dev() has completed. :)

---
Best Regards, Laurentiu