Subject: Re: IBM405GP/GPr OPB bus_space endian (powerpc/ibm4xx/dev/opb.c)
To: Shigeyuki Fukushima <>
From: Simon Burge <>
List: port-powerpc
Date: 10/04/2005 02:03:47
Shigeyuki Fukushima wrote:

> > Your LEDs work fine with the new GPIO framework?  If so, that's good!
> It works fine.
> I could write data 0 to GPIO PIN No.12 by `gpioctl 11 0'.


> > However, I don't like the _ in the name of the gpio_opb device.  We
> > don't have any other devices on any platform that has an underscore in
> > it's name.  Maybe "opbgpio" instead?  It's reasonably normal to use
> > "bus-type device-type" as a naming convention rather than the other way
> > around.
> Ok, I will agree your plan (renaming gpio_opb with opbgpio).
> > I wonder if it is possible to just attach the MI gpio directly to the
> > opb with something like:
> > 	gpio* at opb? addr ? irq ?
> > and
> > 	device	gpio: gpiobus
> > 	attach	gpio at opb with gpio_plb
> > 	file	arch/powerpc/ibm4xx/dev/gpio_opb.c	gpio
> > and drop the intermediate gpio_opb/opbgpio/whatever device?
> It seems that this syntax is invalid.
> /usr/src/sys/arch/powerpc/conf/files.ibm4xx:33: redifinition of `gpio'
> /usr/src/sys/arch/powerpc/conf/files.ibm4xx:34: redifinition of `gpio'
> /usr/src/sys/arch/evbppc/conf/OPENBLOCKS266:169: `gpio' cannot attach to
>  `opb'.

Jared and Quentin (both CC'd here) have some ideas on directly attaching
the gpio to the opb.  Jared set up the net4801 (i386) so that the gpio
was directly attached to the PCI-ISA bridge.  I'll let them speak up
about that.

> >>Why it is Little-Endian in spite of CPU byte-order (Big-Endian) ?
> >>Is there any special reason?
> > After a little look, I'm not really sure!  If you look at
> > powerpc/powerpc/bus_space.c, you'll see that both the little- and
> > big-endian setup in bus_space_init() are exactly the same.  You'd
> > certainly think for most devices on a PPC cpu would be big-endian :-)
> > As I said above, because the setup code is identical, so it
> > shouldn't actually make a difference.  We should audit the calls of
> > bus_space_init() and fix bus_space_init() itself.
> But, the result of bus_space_{read,write}_4 function is *not* the same.
> The return value is littel-endian when calling bus_space_init() with
> For exmaple,
> u_int32_t data;
> data = bus_space_read_4(sc->sc_gpio_iot, sc->sc_gpio_ioh, GPIO_IR);
> printf("data is 0x%x\n");
> Big-endian output is:
> data is 0x00112233
> Littel-endian output is:
> data is 0x33221100

This I'm now totally confused about!  I'll have another look at it

Simon Burge                            <>
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