linux-kernel - Re: [PATCH v2 3/3] arch/*/: remove CONFIG_VIRT_TO

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Date:   Sun, 26 Jun 2022 10:36:02 +0200
From:   Arnd Bergmann <arnd@...nel.org>
To:     Michael Schmitz <schmitzmic@...il.com>
Cc:     linux-scsi <linux-scsi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Jakub Kicinski <kuba@...nel.org>,
        Christoph Hellwig <hch@...radead.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>,
        "open list:IOMMU DRIVERS" <iommu@...ts.linux-foundation.org>,
        Khalid Aziz <khalid@...ehiking.org>,
        "Maciej W . Rozycki" <macro@...am.me.uk>,
        Matt Wang <wwentao@...are.com>,
        Miquel van Smoorenburg <mikevs@...all.net>,
        Mark Salyzyn <salyzyn@...roid.com>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        alpha <linux-alpha@...r.kernel.org>,
        linux-m68k <linux-m68k@...ts.linux-m68k.org>,
        Parisc List <linux-parisc@...r.kernel.org>,
        Denis Efremov <efremov@...ux.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Michael Ellerman <mpe@...erman.id.au>
Subject: Re: [PATCH v2 3/3] arch/*/: remove CONFIG_VIRT_TO_BUS

(On Sun, Jun 26, 2022 at 7:21 AM Michael Schmitz <schmitzmic@...il.com> wrote:
>  > The same could be done for the two vme drivers (scsi/mvme147.c
> > and ethernet/82596.c), which do the cache management but
> > apparently don't need swiotlb bounce buffering.
> >
> > Rewriting the drivers to modern APIs is of course non-trivial,
> > and if you want a shortcut here, I would suggest introducing
> > platform specific helpers similar to isa_virt_to_bus() and call
> > them amiga_virt_to_bus() and vme_virt_to_bus, respectively.
>
> I don't think Amiga and m68k VME differ at all in that respect, so might
> just call it m68k_virt_to_bus() for now.
>
> > Putting these into a platform specific header file at least helps
> > clarify that both the helper functions and the drivers using them
> > are non-portable.
>
> There are no platform specific header files other than asm/amigahw.h and
> asm/mvme147hw.h, currently only holding register address definitions.
> Would it be OK to add m68k_virt_to_bus() in there if it can't remain in
> asm/virtconvert.h, Geert?

In that case, I would just leave it under the current name and not change
m68k at all. I don't like the m68k_virt_to_bus() name because there is
not anything CPU specific in what it does, and keeping it in a common
header does nothing to prevent it from being used on other platforms
either.

> >> 32bit powerpc is a different matter though.
> >
> > It's similar, but unrelated. The two apple ethernet drivers
> > (bmac and mace) can again either get changed to use the
> > dma-mapping interfaces, or get a custom pmac_virt_to_bus()/
> > pmac_bus_to_virt() helper.
>
> Hmmm - I see Finn had done the DMA API conversion on macmace.c which
> might give some hints on what to do about mace.c ... no idea about
> bmac.c though. And again, haven't got hardware to test, so custom
> helpers is it, then.

Ok.

          Arnd