Re: [PATCH 00/21] SMMU enablement for NXP LS1043A and LS1046A

[Laurentiu Tudor <laurentiu.tudor@nxp.com>]

On 19.09.2018 17:37, Robin Murphy wrote:
> On 19/09/18 15:18, Laurentiu Tudor wrote:
>> Hi Robin,
>>
>> On 19.09.2018 16:25, Robin Murphy wrote:
>>> Hi Laurentiu,
>>>
>>> On 19/09/18 13:35, laurentiu.tudor@nxp.com wrote:
>>>> From: Laurentiu Tudor <laurentiu.tudor@nxp.com>
>>>>
>>>> This patch series adds SMMU support for NXP LS1043A and LS1046A chips
>>>> and consists mostly in important driver fixes and the required device
>>>> tree updates. It touches several subsystems and consists of three main
>>>> parts:
>>>>    - changes in soc/drivers/fsl/qbman drivers adding iommu mapping of
>>>>      reserved memory areas, fixes and defered probe support
>>>>    - changes in drivers/net/ethernet/freescale/dpaa_eth drivers
>>>>      consisting in misc dma mapping related fixes and probe ordering
>>>>    - addition of the actual arm smmu device tree node together with
>>>>      various adjustments to the device trees
>>>>
>>>> Performance impact
>>>>
>>>>       Running iperf benchmarks in a back-to-back setup (both sides
>>>>       having smmu enabled) on a 10GBps port show an important
>>>>       networking performance degradation of around %40 (9.48Gbps
>>>>       linerate vs 5.45Gbps). If you need performance but without
>>>>       SMMU support you can use "iommu.passthrough=1" to disable
>>>>       SMMU.
>>>>
>>>> USB issue and workaround
>>>>
>>>>       There's a problem with the usb controllers in these chips
>>>>       generating smaller, 40-bit wide dma addresses instead of the 
>>>> 48-bit
>>>>       supported at the smmu input. So you end up in a situation 
>>>> where the
>>>>       smmu is mapped with 48-bit address translations, but the device
>>>>       generates transactions with clipped 40-bit addresses, thus smmu
>>>>       context faults are triggered. I encountered a similar 
>>>> situation for
>>>>       mmc that I  managed to fix in software [1] however for USB I 
>>>> did not
>>>>       find a proper place in the code to add a similar fix. The only
>>>>       workaround I found was to add this kernel parameter which 
>>>> limits the
>>>>       usb dma to 32-bit size: "xhci-hcd.quirks=0x800000".
>>>>       This workaround if far from ideal, so any suggestions for a code
>>>>       based workaround in this area would be greatly appreciated.
>>>
>>> If you have a nominally-64-bit device with a
>>> narrower-than-the-main-interconnect link in front of it, that should
>>> already be fixed in 4.19-rc by bus_dma_mask picking up DT dma-ranges,
>>> provided the interconnect hierarchy can be described appropriately (or
>>> at least massaged sufficiently to satisfy the binding), e.g.:
>>>
>>> / {
>>>       ...
>>>
>>>       soc {
>>>           ranges;
>>>           dma-ranges = <0 0 10000 0>;
>>>
>>>           dev_48bit { ... };
>>>
>>>           periph_bus {
>>>               ranges;
>>>               dma-ranges = <0 0 100 0>;
>>>
>>>               dev_40bit { ... };
>>>           };
>>>       };
>>> };
>>>
>>> and if that fails to work as expected (except for PCI hosts where
>>> handling dma-ranges properly still needs sorting out), please do let us
>>> know ;)
>>>
>>
>> Just to confirm, Is this [1] the change I was supposed to test?
> 
> Not quite - dma-ranges is only valid for nodes representing a bus, so 
> putting it directly in the USB device nodes doesn't work (FWIW that's 
> why PCI is broken, because the parser doesn't expect the 
> bus-as-leaf-node case). That's teh point of that intermediate simple-bus 
> node represented by "periph_bus" in my example (sorry, I should have put 
> compatibles in to make it clearer) - often that's actually true to life 
> (i.e. "soc" is something like a CCI and "periph_bus" is something like 
> an AXI NIC gluing a bunch of lower-bandwidth DMA masters to one of the 
> CCI ports) but at worst it's just a necessary evil to make the binding 
> happy (if it literally only represents the point-to-point link between 
> the device master port and interconnect slave port).
> 

Quick update: so I adjusted to device tree according to your example and 
it works so now I can get rid of that nasty kernel arg based workaround, 
yey! :-)
Thanks a lot, that was really helpful.

---
Best Regards, Laurentiu