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

[Laurentiu Tudor]

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. :)

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Best Regards, Laurentiu