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@xxxxxxx wrote:
>>>> From: Laurentiu Tudor <laurentiu.tudor@xxxxxxx>
>>>>
>>>> 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
