linux-kernel - Re: [PATCH] [v4] m68k: coldfire: drop ISA_DMA

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Date:   Fri, 22 Apr 2022 11:01:03 +0200
From:   Arnd Bergmann <arnd@...nel.org>
To:     Michael Schmitz <schmitzmic@...il.com>
Cc:     Greg Ungerer <gerg@...ux-m68k.org>, Arnd Bergmann <arnd@...db.de>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        linux-m68k <linux-m68k@...ts.linux-m68k.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-mmc <linux-mmc@...r.kernel.org>,
        ALSA Development Mailing List <alsa-devel@...a-project.org>
Subject: Re: [PATCH] [v4] m68k: coldfire: drop ISA_DMA_API support

On Fri, Apr 22, 2022 at 9:48 AM Michael Schmitz <schmitzmic@...il.com> wrote:
> Am 21.04.2022 um 20:20 schrieb Arnd Bergmann:
> > From: Arnd Bergmann <arnd@...db.de>
> >
> > After a build regression report, I took a look at possible users of
> > CONFIG_ISA_DMA_API on m68k and found none, which Greg confirmed. The
> > CONFIG_GENERIC_ISA_DMA option in turn is only needed to implement
> > ISA_DMA_API, and is clearly not used on the platforms with ISA support.
> >
> > The CONFIG_ISA support for AMIGA_PCMCIA is probably also unneeded,
> > but this is less clear. Unlike other PCMCIA implementations, this one
> > does not use the drivers/pcmcia subsystem at all and just supports
> > the "apne" network driver. When it was first added, one could use
> > ISA drivers on it as well, but this probably broke at some point.
>
> Hoping to clarify some of this:
>
> For the Amiga PCMCIA "apne" driver, both the definitions of
> isa_type/isa_sex and the definitions of the low-level accessor and
> address translation functions are protected by CONFIG_ISA (see
> arch/m68k/kernel/setup_mm.c and arch/m68k/include/asm/io_mm.h for details).
>
> This could conceivably be changed (only AMIGA_PCMCIA and Q40 do use
> these definitions, aside from ATARI_ROM_ISA), but as things are right
> now, neither Q40 ISA nor Amiga PCMCIA will work without CONFIG_ISA defined.

Ok, thanks for clarifying that, this makes a lot more sense now. I was wondering
what ISA devices one can actually use without DMA, but it turns out that a
lot of the older storage (pata_legacy, pata_isapnp, aha152x) and network
(3c509, 8390, cs89x0, smc9194) devices work in PIO mode, aside from
a couple of oddball special-purpose stuff (speech, busmouse, comedi,
appletalk, wan, ...).

> Regarding the Amiga PCMCIA driver's use of the drivers/pcmcia subsystem,
> I have a patch in limbo at netdev that makes use of the cftable parser
> code from drivers/pcmcia, but as far as I can recall, none of this
> depends on CONFIG_ISA.

Yes, Geert mentioned that on IRC already. Note that Dominik Brodowski
has said in the past that he would plan to eventually drop PCMCIA
support from the kernel, but I think if that happens, the cftable
parser can just be moved into the amiga_pcmcia code.

       Arnd