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

On 19.09.2018 17:37, Robin Murphy wrote:

On 19/09/18 15:18, Laurentiu Tudor wrote:

quoted

Hi Robin,

On 19.09.2018 16:25, Robin Murphy wrote:

quoted

Hi Laurentiu,

On 19/09/18 13:35, laurentiu.tudor at nxp.com wrote:

quoted

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