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Re: usb: dwc2: regression on MyBook Live Duo / Canyonlands since 4.3.0-rc4

From Benjamin Herrenschmidt <benh@kernel.crashing.org>
Newsgroups linux.kernel
Subject Re: usb: dwc2: regression on MyBook Live Duo / Canyonlands since 4.3.0-rc4
Date 2016-05-13 00:20 +0200
Message-ID <ry77z-6Pl-5@gated-at.bofh.it> (permalink)
References <rwvnI-6dm-7@gated-at.bofh.it> <rx20i-6qo-7@gated-at.bofh.it> <rxahc-69M-11@gated-at.bofh.it> <rxVzt-30G-13@gated-at.bofh.it>
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On Thu, 2016-05-12 at 11:58 +0200, Christian Lamparter wrote:
> 
> > http://www.linuxplumbersconf.org/2012/wp-content/uploads/2012/09/2012-lpc-ref-big-little-endian-herrenschmidt.odp
> > 
> > but there are at least two more twists that you completely missed here:
> > 
> > - Some architectures (e.g. ARMv5 "BE32" mode in IXP4xx, surely some others)
> >   do not implement big-endian mode by wiring up the data lines between the
> >   bus and the CPU differently between big- and little-endian mode like
> >   powerpc and armv7 "BE8" do, but instead they swizzle the *address* lines
> >   on 8-bit and 16-bit addresses. The effect of that is that normal RAM
> >   accesses work as expected both ways, and devices that are accessed using
> >   32-bit MMIO ops never need any byteswap (you actually get "native
> >   endian") while MMIO with 8 and 16 bit width does something completely
> >   unexpected and touches the wrong register. Having an explicit byteswap
> >   on the PCI host bridge gets you the expected addresses again for 8-bit
> >   cycles but it also means that readl()/writel() again need to swap the
> >   data.

Right. Old PowerPC did that too and it's completely stupid. Thankfully
most vendors grew a clue since then and this practice has slowly fallen
into oblivion.

> > - Some other architectures (e.g. Broadcom MIPS) apparently are even fancier
> >   and use a strapping pin on the SoC flips the endianess of the CPU core
> >   at the same time as all the peripheral MMIO registers, with the intention
> >   of never requiring any byte swaps. I believe they are implemented careful
> >   enough to actually get this right, but it confuses the heck out of
> >   Linux drivers that don't expect this.

Right. Drivers like that will need an explicit test in the accessors.

Cheers,
Ben.

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Re: usb: dwc2: regression on MyBook Live Duo / Canyonlands since 4.3.0-rc4 Christian Lamparter <chunkeey@googlemail.com> - 2016-05-08 13:50 +0200
  Re: usb: dwc2: regression on MyBook Live Duo / Canyonlands since  4.3.0-rc4 Benjamin Herrenschmidt <benh@au1.ibm.com> - 2016-05-09 02:30 +0200
    Re: usb: dwc2: regression on MyBook Live Duo / Canyonlands since 4.3.0-rc4 Arnd Bergmann <arnd@arndb.de> - 2016-05-09 12:40 +0200
      Re: usb: dwc2: regression on MyBook Live Duo / Canyonlands since 4.3.0-rc4 Felipe Balbi <felipe.balbi@linux.intel.com> - 2016-05-09 12:50 +0200
        Re: usb: dwc2: regression on MyBook Live Duo / Canyonlands since 4.3.0-rc4 Arnd Bergmann <arnd@arndb.de> - 2016-05-09 17:10 +0200
          Re: usb: dwc2: regression on MyBook Live Duo / Canyonlands since 4.3.0-rc4 Arnd Bergmann <arnd@arndb.de> - 2016-05-09 22:20 +0200
          Re: usb: dwc2: regression on MyBook Live Duo / Canyonlands since  4.3.0-rc4 Benjamin Herrenschmidt <benh@kernel.crashing.org> - 2016-05-10 00:40 +0200
            Re: usb: dwc2: regression on MyBook Live Duo / Canyonlands since 4.3.0-rc4 Arnd Bergmann <arnd@arndb.de> - 2016-05-10 09:30 +0200
              Re: usb: dwc2: regression on MyBook Live Duo / Canyonlands since 4.3.0-rc4 Christian Lamparter <chunkeey@googlemail.com> - 2016-05-12 12:00 +0200
                Re: usb: dwc2: regression on MyBook Live Duo / Canyonlands since 4.3.0-rc4 Arnd Bergmann <arnd@arndb.de> - 2016-05-12 14:00 +0200
                Re: usb: dwc2: regression on MyBook Live Duo / Canyonlands since 4.3.0-rc4 Christian Lamparter <chunkeey@googlemail.com> - 2016-05-12 15:40 +0200
                Re: usb: dwc2: regression on MyBook Live Duo / Canyonlands since  4.3.0-rc4 John Youn <John.Youn@synopsys.com> - 2016-05-12 20:50 +0200
                Re: usb: dwc2: regression on MyBook Live Duo / Canyonlands since 4.3.0-rc4 Christian Lamparter <chunkeey@googlemail.com> - 2016-05-12 22:40 +0200
                Re: usb: dwc2: regression on MyBook Live Duo / Canyonlands since 4.3.0-rc4 Arnd Bergmann <arnd@arndb.de> - 2016-05-12 23:00 +0200
                Re: usb: dwc2: regression on MyBook Live Duo / Canyonlands since  4.3.0-rc4 John Youn <John.Youn@synopsys.com> - 2016-05-12 23:00 +0200
                Re: usb: dwc2: regression on MyBook Live Duo / Canyonlands since 4.3.0-rc4 Arnd Bergmann <arnd@arndb.de> - 2016-05-14 21:50 +0200
                Re: usb: dwc2: regression on MyBook Live Duo / Canyonlands since  4.3.0-rc4 John Youn <John.Youn@synopsys.com> - 2016-05-18 02:00 +0200
                Re: usb: dwc2: regression on MyBook Live Duo / Canyonlands since 4.3.0-rc4 Christian Lamparter <chunkeey@googlemail.com> - 2016-05-18 21:20 +0200
                Re: usb: dwc2: regression on MyBook Live Duo / Canyonlands since 4.3.0-rc4 Arnd Bergmann <arnd@arndb.de> - 2016-05-18 23:10 +0200
                Re: usb: dwc2: regression on MyBook Live Duo / Canyonlands since  4.3.0-rc4 John Youn <John.Youn@synopsys.com> - 2016-05-19 02:40 +0200
                Re: usb: dwc2: regression on MyBook Live Duo / Canyonlands since  4.3.0-rc4 Benjamin Herrenschmidt <benh@kernel.crashing.org> - 2016-05-13 00:20 +0200
          Re: usb: dwc2: regression on MyBook Live Duo / Canyonlands since  4.3.0-rc4 Benjamin Herrenschmidt <benh@kernel.crashing.org> - 2016-05-10 00:50 +0200
        Re: usb: dwc2: regression on MyBook Live Duo / Canyonlands since  4.3.0-rc4 Benjamin Herrenschmidt <benh@kernel.crashing.org> - 2016-05-10 00:40 +0200
      Re: usb: dwc2: regression on MyBook Live Duo / Canyonlands since  4.3.0-rc4 Benjamin Herrenschmidt <benh@au1.ibm.com> - 2016-05-09 16:10 +0200
      Re: usb: dwc2: regression on MyBook Live Duo / Canyonlands since  4.3.0-rc4 John Youn <John.Youn@synopsys.com> - 2016-05-09 22:30 +0200
        Re: usb: dwc2: regression on MyBook Live Duo / Canyonlands since 4.3.0-rc4 Arnd Bergmann <arnd@arndb.de> - 2016-05-09 22:40 +0200
          Re: usb: dwc2: regression on MyBook Live Duo / Canyonlands since  4.3.0-rc4 John Youn <John.Youn@synopsys.com> - 2016-05-09 23:20 +0200
            Re: usb: dwc2: regression on MyBook Live Duo / Canyonlands since 4.3.0-rc4 Arnd Bergmann <arnd@arndb.de> - 2016-05-09 23:40 +0200

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