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Subject: Re: [PATCHv9 00/12] PCI: Recode Mobiveil driver and add PCIe Gen4
 driver for NXP Layerscape SoCs
To:     Laurentiu Tudor <laurentiu.tudor@nxp.com>,
        Li Yang <leoyang.li@nxp.com>, Olof Johansson <olof@lixom.net>
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From:   Robin Murphy <robin.murphy@arm.com>
Message-ID: <aec47903-50e4-c61b-6aec-63e3e9bc9332@arm.com>
Date:   Tue, 11 Feb 2020 13:04:14 +0000
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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) :)

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).

> In the mean time, can you try the workaround Leo suggested?

Agreed, I'd imagine the command-line option is probably the best choice 
for these platforms, since it's likely to be easier to set that by 
default in the bootloader than faff with rebuilding generic kernel configs.

Robin.

> [1] https://patchwork.kernel.org/patch/11327667/
> [2] https://patchwork.kernel.org/patch/10967729/
> [3] https://patchwork.kernel.org/cover/11279577/
> 
> ---
> Best Regards, Laurentiu
> 
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