linux-kernel - Re: [PATCH 0/1] m68k: Handle HAS

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Message-ID: <CAMuHMdX026rLnJP2K-MhBjzVnmu8EReYe3PJc595Vjp4GoBK7w@mail.gmail.com>
Date: Mon, 8 Apr 2024 10:23:25 +0200
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Arnd Bergmann <arnd@...nel.org>
Cc: Michael Schmitz <schmitzmic@...il.com>, Niklas Schnelle <schnelle@...ux.ibm.com>, 
	linux-m68k@...ts.linux-m68k.org, Heiko Carstens <hca@...ux.ibm.com>, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/1] m68k: Handle HAS_IOPORT dependencies

Hi Arnd,

On Fri, Apr 5, 2024 at 1:26 PM Arnd Bergmann <arnd@...nel.org> wrote:
> On Fri, Apr 5, 2024, at 12:16, Geert Uytterhoeven wrote:
> > On Wed, Apr 3, 2024 at 8:35 PM Arnd Bergmann <arnd@...nel.org> wrote:
> > Michael is worried about non-ISA drivers using inb() and friends.
> > At some point in time (i.e. eons ago), we were told it was better to
> > use in[bwl]()/read[bwl]() instead of directly dereferencing volatile
> > pointers...
>
> It's definitely still better to use an abstraction layer for MMIO
> accesses using inline asm instructions than open-coding the
> volatile pointer dereferences. Over time we have gotten better
> at defining which of the available abstractions should be used
> for a given bus, so inb()/outb() is now only really used for
> things derived from ISA in some form, including e.g. PCI and LPC.

Indeed. Nowadays the consensus is that readl() and friends should
always perform little-endian accesses, thus implying byte-swapping on
big-endian platforms, but most of the m68k drivers were written long
before that enlightenment...

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68korg

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