netdev - Re: Is drivers/net/wan/lmc dead?

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Date:   Mon, 21 Mar 2022 23:10:32 +0100
From:   Arnd Bergmann <arnd@...nel.org>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     Krzysztof Hałasa <khalasa@...p.pl>,
        Andrew Stanley-Jones <asj@...n.com>,
        Rob Braun <bbraun@....com>, Michael Graff <explorer@....com>,
        Matt Thomas <matt@...-software.com>,
        Krzysztof Halasa <khc@...waw.pl>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: Is drivers/net/wan/lmc dead?

On Mon, Mar 21, 2022 at 10:40 PM Jakub Kicinski <kuba@...nel.org> wrote:
>
> Hi!
>
> The driver for LAN Media WAN interfaces spews build warnings on
> microblaze.
>
> CCing usual suspects and people mentioned as authors in the source code.
>
> As far as I can tell it has no maintainer.
>
> It has also received not received a single functional change that'd
> indicate someone owns this HW since the beginning of the git era.
>
> Can we remove this driver or should we invest effort into fixing it?

I have not seen the exact error, but I suspect the problem is that
microblaze selects CONFIG_VIRT_TO_BUS without actually
providing those interfaces. The easy workaround would be to
have microblaze not select that symbol.

Drivers using virt_to_bus() are inherently nonportable because
they don't work on architectures that use an IOMMU or swiotlb,
or that require cache maintenance for DMA operations.

$ git grep -wl virt_to_bus drivers/
drivers/atm/ambassador.c
drivers/atm/firestream.c
drivers/atm/horizon.c
drivers/atm/zatm.c
drivers/block/swim3.c
drivers/gpu/drm/mga/mga_dma.c
drivers/net/appletalk/ltpc.c
drivers/net/ethernet/amd/au1000_eth.c
drivers/net/ethernet/amd/ni65.c
drivers/net/ethernet/apple/bmac.c
drivers/net/ethernet/apple/mace.c
drivers/net/ethernet/dec/tulip/de4x5.c
drivers/net/ethernet/i825xx/82596.c
drivers/net/ethernet/i825xx/lasi_82596.c
drivers/net/ethernet/i825xx/lib82596.c
drivers/net/hamradio/dmascc.c
drivers/net/wan/cosa.c
drivers/net/wan/lmc/lmc_main.c
drivers/net/wan/z85230.c
drivers/scsi/3w-xxxx.c
drivers/scsi/a2091.c
drivers/scsi/a3000.c
drivers/scsi/dpt_i2o.c
drivers/scsi/gvp11.c
drivers/scsi/mvme147.c
drivers/scsi/qla1280.c
drivers/tty/serial/cpm_uart/cpm_uart_cpm2.c
drivers/vme/bridges/vme_ca91cx42.c

Among the drivers/net/wan/ drivers, I think lmc is actually
one of the newer pieces of hardware, most of the other ones
appear to even predate PCI.

        Arnd