[PATCH v6 5/6] fbdev: Move framebuffer I/O helpers into <asm/fb.h>

[Geert Uytterhoeven]

Hi Arnd,

CC Artur, who's working on HP Jornada 680.

On Wed, May 10, 2023 at 5:55 PM Arnd Bergmann <arnd at arndb.de> wrote:
> On Wed, May 10, 2023, at 16:27, Thomas Zimmermann wrote:
> > Am 10.05.23 um 16:15 schrieb Arnd Bergmann:
> >> On Wed, May 10, 2023, at 16:03, kernel test robot wrote:
>
> >> I think that's a preexisting bug and I have no idea what the
> >> correct solution is. Looking for HD64461 shows it being used
> >> both with inw/outw and readw/writew, so there is no way to have
> >> the correct type. The sh __raw_readw() definition hides this bug,
> >> but that is a problem with arch/sh and it probably hides others
> >> as well.
> >
> > The constant HD64461_IOBASE is defined as integer at
> >
> >
> > https://elixir.bootlin.com/linux/latest/source/arch/sh/include/asm/hd64461.h#L17
> >
> > but fb_readw() expects a volatile-void pointer. I guess we could add a
> > cast somewhere to silence the problem. In the current upstream code,
> > that appears to be done by sh's __raw_readw() internally:
> >
> >
> > https://elixir.bootlin.com/linux/latest/source/arch/sh/include/asm/io.h#L35
>
> Sure, that would make it build again, but that still doesn't make the
> code correct, since it's completely unclear what base address the
> HD64461_IOBASE is relative to. The hp6xx platform code only passes it
> through inw()/outw(), which take an offset relative to sh_io_port_base,
> but that is not initialized on hp6xx. I tried to find in the history
> when it broke, apparently that was in 2007 commit 34a780a0afeb ("sh:
> hp6xx pata_platform support."), which removed the custom inw/outw
> implementations.

See also commit 4aafae27d0ce73f8 ("sh: hd64461 tidying."), which
claims they are no longer needed.

Don't the I/O port macros just treat the port as an absolute base address
when sh_io_port_base isn't set?

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