Date:   Fri, 21 Sep 2018 07:32:12 +0000
From:   Laurentiu Tudor <laurentiu.tudor@....com>
To:     Leo Li <leoyang.li@....com>
CC:     "robin.murphy@....com" <robin.murphy@....com>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>, Netdev <netdev@...r.kernel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>,
        Madalin-cristian Bucur <madalin.bucur@....com>,
        Roy Pledge <roy.pledge@....com>,
        Shawn Guo <shawnguo@...nel.org>,
        David Miller <davem@...emloft.net>
Subject: RE: [PATCH 00/21] SMMU enablement for NXP LS1043A and LS1046A



> -----Original Message-----
> From: Li Yang [mailto:leoyang.li@....com]
> Sent: Thursday, September 20, 2018 10:07 PM
> 
> On Thu, Sep 20, 2018 at 5:39 AM Laurentiu Tudor <laurentiu.tudor@....com>
> wrote:
> >
> >
> >
> > 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@....com wrote:
> > >>>> From: Laurentiu Tudor <laurentiu.tudor@....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! :-)
> 
> Great that we have a generic solution like I hoped for!  So you will
> submit a new revision of the series to include these dts updates,
> right?
> 

Yes, I already have it prepared. Just delaying the v2 for a few days maybe there will be some more feedback.

---
Best Regards, Laurentiu

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