Re: [PATCH 3/3] net: smsc911x: add u16 workaround for pxa platforms

From	Rob Herring <robh@kernel.org>
Newsgroups	linux.kernel
Subject	Re: [PATCH 3/3] net: smsc911x: add u16 workaround for pxa platforms
Date	2016-10-09 03:40 +0200
Message-ID	<sqbfQ-6a9-7@gated-at.bofh.it> (permalink)
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On Thu, Oct 06, 2016 at 08:47:13AM +0200, Robert Jarzmik wrote:
> Robert Jarzmik <robert.jarzmik@free.fr> writes:
> 
> > Mark Rutland <mark.rutland@arm.com> writes:
> >
> >> On Mon, Oct 03, 2016 at 06:11:23PM +0200, Robert Jarzmik wrote:
> >>> Mark Rutland <mark.rutland@arm.com> writes:
> >>> 
> >>> reg-u16-align4 tells that a specific hardware doesn't support 16 bit writes not
> >>> being 32 bits aligned, or said differently that a "store" 16 bits wide on an
> >>> address of the format 4*n + 2 deserves a special handling in the driver, while a
> >>> store 16 bits wide on an address of the format 4*n can follow the simple casual
> >>> case.
> >>
> >> If I've understood correctly, effectively the low 2 address lines to the
> >> device are hard-wired to zero, e.g. a 16-bit access to 4*n + 2 would go
> >> to 4*n + 0 on the device? Or is the failure case distinct from that?
> > It is distinct.
> >
> > The "awful truth" is that an FPGA lies between the system bus and the
> > smc91c111. And this FPGA cannot handle correctly the 4*n + 2 u16 writes.
> >
> >> Do we have other platforms where similar is true? e.g. u8 accesses
> >> requiring 16-bit alignment?
> >
> > Not really, ie. not with a alignement requirement.
> >
> > But there are of course these ones are handled by reg-io-width and the
> > SMC_USE_xxx_BITS flags as far as I understand it. These cases are when a
> > platform declares SMC91X_USE_16BIT or SMC91X_USE_32BIT, but not SMC91X_USE_8BIT,
> > which would make me think of :
> >  - CONFIG_SH_SH4202_MICRODEV,
> >  - CONFIG_M32R
> >  - several omap1 boards
> >  - 1 sa1100 board
> >  - several MMP and realview boards
> >
> > With all these platforms, each u8 access is replaced with a u16 access and a
> > mask / shift + mask.
> 
> Or so what should I call this entry if reg-u16-align4 is not a good candidate ?

This seems broken in a very platform specific way, so perhaps something 
named based on the platform.

Rob

Thread

[PATCH 3/3] net: smsc911x: add u16 workaround for pxa platforms Robert Jarzmik <robert.jarzmik@free.fr> - 2016-10-03 11:10 +0200
  Re: [PATCH 3/3] net: smsc911x: add u16 workaround for pxa platforms Jeremy Linton <jeremy.linton@arm.com> - 2016-10-03 17:30 +0200
    Re: [PATCH 3/3] net: smsc911x: add u16 workaround for pxa platforms Robert Jarzmik <robert.jarzmik@free.fr> - 2016-10-03 18:20 +0200
  Re: [PATCH 3/3] net: smsc911x: add u16 workaround for pxa platforms Mark Rutland <mark.rutland@arm.com> - 2016-10-03 17:50 +0200
    Re: [PATCH 3/3] net: smsc911x: add u16 workaround for pxa platforms Robert Jarzmik <robert.jarzmik@free.fr> - 2016-10-03 18:20 +0200
      Re: [PATCH 3/3] net: smsc911x: add u16 workaround for pxa platforms Mark Rutland <mark.rutland@arm.com> - 2016-10-03 19:00 +0200
        Re: [PATCH 3/3] net: smsc911x: add u16 workaround for pxa platforms Robert Jarzmik <robert.jarzmik@free.fr> - 2016-10-03 21:20 +0200
          Re: [PATCH 3/3] net: smsc911x: add u16 workaround for pxa platforms Robert Jarzmik <robert.jarzmik@free.fr> - 2016-10-06 08:50 +0200
            Re: [PATCH 3/3] net: smsc911x: add u16 workaround for pxa platforms Rob Herring <robh@kernel.org> - 2016-10-09 03:40 +0200
    Re: [PATCH 3/3] net: smsc911x: add u16 workaround for pxa platforms Russell King - ARM Linux <linux@armlinux.org.uk> - 2016-10-03 18:20 +0200
      Re: [PATCH 3/3] net: smsc911x: add u16 workaround for pxa platforms Mark Rutland <mark.rutland@arm.com> - 2016-10-03 18:50 +0200
        Re: [PATCH 3/3] net: smsc911x: add u16 workaround for pxa platforms Rob Herring <robh@kernel.org> - 2016-10-09 03:40 +0200

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