[PATCH 2/7] ARM: shmobile: r8a7779: Use ioremap() to map INTC2 registers

[Geert Uytterhoeven]

Hi Arnd,

On Tue, Nov 17, 2020 at 4:06 PM Arnd Bergmann <arnd at kernel.org> wrote:
> On Tue, Nov 17, 2020 at 3:47 PM Geert Uytterhoeven <geert at linux-m68k.org> wrote:
> > On Tue, Nov 17, 2020 at 3:39 PM Arnd Bergmann <arnd at kernel.org> wrote:
> > > On Tue, Nov 17, 2020 at 3:19 PM Geert Uytterhoeven <geert at linux-m68k.org> wrote:
> > > > On Tue, Nov 17, 2020 at 1:25 PM Arnd Bergmann <arnd at kernel.org> wrote:
> > > > > On Tue, Nov 17, 2020 at 11:30 AM Geert Uytterhoeven
> > > > > <geert+renesas at glider.be> wrote:
> > > > > > Replace using the legacy IOMEM() macro to map various registers related
> > > > > > to INTC2 configuration by ioremap().
> > > > > >
> > > > > > Signed-off-by: Geert Uytterhoeven <geert+renesas at glider.be>
> > > > >
> > > > > The patch looks good, but since you are already touching these __raw_writel(),
> > > > > could you turn them into normal writel() to have a chance that this works
> > > > > on big-endian? It could be either a follow-up or merged into the same patch.
> > > >
> > > > (Do you want us to support big-endian on these old platforms? ;-)
> > > >
> > > > At your service. Seems to work well.
> > >
> > > In general, my preference is that code is written in a portable way, to make
> > > it at least plausible that it works. I don't expect anyone to actually run
> > > big-endian code on it, but if you can confirm that it boots all the way
> > > to not finding a compatible /sbin/init, that would be awesome.
> >
> > With "work well", I meant no regressions after converting from _raw_*()
> > to normal accessors.  No idea how to boot big-endian kernels on this
> > hardware ;-)
>
> There is no change when booting them, you just enable
> CONFIG_CPU_BIG_ENDIAN and recompile the kernel.

And have to select ARCH_SUPPORTS_BIG_ENDIAN first...

> The bootloader remains little-endian and the first instruction in
> the image then changes into big-endian mode. The expected
> behavior is that it crashes as soon as it tries to get into user

Cool!

SH-Mobile AG5 boots until trying to power off the A3R power domain.
After converting the __raw_*() accessors in
drivers/soc/renesas/rmobile-sysc.c and drivers/clk/renesas/clk-sh73a0.c
it continues until /sbin/init fails, as expected.

R-Car M2-W boots until DHCP timeout.  Could be due to either sh_eth or
the micrel PHY driver, or MDIO (replacing io{read,write}32() by
{read,write}l() in sh_eth.c doesn't help).

Note that drivers/tty/serial/8250/8250_dw.c, which is used on RZ/N1,
uses __raw_{write,read}q(), too.

So I guess it's a bit too early to enable ARCH_SUPPORTS_BIG_ENDIAN
unconditionally.

> space. Recompiling that is significantly more work.

Doh, and even Debian ports doesn't support armeb anymore, else it
would just be a debootstrap away...


Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert at linux-m68k.org

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