Hi Arnd,
On Thu, Nov 19, 2020 at 5:22 PM Arnd Bergmann <arnd@xxxxxxxxxx> wrote:
> On Thu, Nov 19, 2020 at 5:13 PM Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> wrote:
> > On Thu, Nov 19, 2020 at 4:54 PM Arnd Bergmann <arnd@xxxxxxxxxx> wrote:
> > > On Thu, Nov 19, 2020 at 1:53 PM Geert Uytterhoeven
> > > <geert+renesas@xxxxxxxxx> wrote:
> > >
> > > I'm also not sure whether changing this breaks big-endian SuperH,
> > > which defines the accessors differently from Arm and most other
> > > architectures.
> >
> > On SH, this driver is only used on SH7724 systems.
> > Compiling an ecovec24_defconfig kernel with CONFIG_CPU_BIG_ENDIAN=y
> > shows that the same code (native 32-bit access) is generated for
> > big-endian as for little-endian, which means that it indeed must be
> > broken for one of them. But this is not changed by my patch.
>
> Not necessarily: I think superh is more like the old 'BE32' variant of Arm
> big-endian, in that on-chip registers are accessed in CPU-endian byte order,
> while access to external RAM is byte-swapped.
That's indeed quite likely: according to the SH7724 docs, the endianness
of "the system" is configured by an external pin at power-on reset time,
and cannot be changed dynamically. Hence testing this would require a
big-endian boot loader, too.
> > > Maybe better just mark the driver as 'depends on SH || !CPU_BIG_ENDIAN'
> > > as it is clearly broken on big-endian Arm.
> >
> > "depends on !CPU_BIG_ENDIAN"?
>
> I think I'd just leave it as it is. Unless someone wants to try out this
OK.
> board in both big-endian and little-endian configurations and also
> listen to the audio output, it's impossible to know whether it is actually
> broken. sound/soc/sh/dma-sh7760.c does have a comment from 2007
> saying "// FIXME: little-endian only for now".
SH7760 does not use the FSI driver.
A few SH defconfig files have CONFIG_CPU_BIG_ENDIAN=y, but
the later SH4A parts all seem to be used in little-endian mode.
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
