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

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Date:   Sat, 18 Jun 2022 13:06:40 +1200
From:   Michael Schmitz <schmitzmic@...il.com>
To:     Arnd Bergmann <arnd@...nel.org>, linux-scsi@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     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>,
        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@...ts.ozlabs.org, linux-arch@...r.kernel.org,
        linux-alpha@...r.kernel.org, linux-m68k@...ts.linux-m68k.org,
        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

Arnd,

Am 18.06.2022 um 00:57 schrieb Arnd Bergmann:
> From: Arnd Bergmann <arnd@...db.de>
>
> All architecture-independent users of virt_to_bus() and bus_to_virt()
> have been fixed to use the dma mapping interfaces or have been
> removed now.  This means the definitions on most architectures, and the
> CONFIG_VIRT_TO_BUS symbol are now obsolete and can be removed.
>
> The only exceptions to this are a few network and scsi drivers for m68k
> Amiga and VME machines and ppc32 Macintosh. These drivers work correctly
> with the old interfaces and are probably not worth changing.

The Amiga SCSI drivers are all old WD33C93 ones, and replacing 
virt_to_bus by virt_to_phys in the dma_setup() function there would 
cause no functional change at all.

drivers/vme/bridges/vme_ca91cx42.c hasn't been used at all on m68k (it 
is a PCI-to-VME bridge chipset driver that would be needed on 
architectures that natively use a PCI bus). I haven't found anything 
that selects that driver, so not sure it is even still in use??

That would allow you to drop the remaining virt_to_bus define from 
arch/m68k/include/asm/virtconvert.h.

I could submit a patch to convert the Amiga SCSI drivers to use 
virt_to_phys if Geert and the SCSI maintainers think it's worth the churn.

32bit powerpc is a different matter though.

Cheers,

	Michael