linux-kernel - Re: [PATCH 05/67] dma-mapping: replace PCI_DMA_BUS_IS_PHYS with a flag in struct dma_map

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Date:   Tue, 2 Jan 2018 11:39:49 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Christoph Hellwig <hch@....de>
Cc:     iommu@...ts.linux-foundation.org,
        Linux MIPS Mailing List <linux-mips@...ux-mips.org>,
        linux-ia64@...r.kernel.org,
        Linux-sh list <linux-sh@...r.kernel.org>,
        sparclinux <sparclinux@...r.kernel.org>,
        Guan Xuetao <gxt@...c.pku.edu.cn>,
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        linux-s390 <linux-s390@...r.kernel.org>,
        linux-c6x-dev@...ux-c6x.org,
        "open list:QUALCOMM HEXAGON..." <linux-hexagon@...r.kernel.org>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        arcml <linux-snps-arc@...ts.infradead.org>,
        adi-buildroot-devel@...ts.sourceforge.net,
        linux-m68k <linux-m68k@...ts.linux-m68k.org>,
        patches@...ups.riscv.org,
        "open list:METAG ARCHITECTURE" <linux-metag@...r.kernel.org>,
        linux-arm-kernel@...ts.infradead.org,
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        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        alpha <linux-alpha@...r.kernel.org>,
        linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH 05/67] dma-mapping: replace PCI_DMA_BUS_IS_PHYS with a
 flag in struct dma_map_ops

On Fri, Dec 29, 2017 at 9:18 AM, Christoph Hellwig <hch@....de> wrote:
> The current PCI_DMA_BUS_IS_PHYS decided if a dma implementation is bound
> by the dma mask in the device because it directly maps to a physical
> address range (modulo an offset in the device), or if it is virtualized
> by an iommu and can map any address (that includes virtual iommus like
> swiotlb).  The problem with this scheme is that it is per-architecture and
> not per dma_ops instance, and we are growing more and more setups that
> have multiple different dma operations in use on a single system, for
> which this scheme can't provide a correct answer.  Depending on the
> architecture that means we either get a false positive or false negative
> at the moment.
>
> This patch instead extents the is_phys flag in struct dma_map_ops that
> is currently only used by a few architectures to be used tree wide.
>
> Note that this means that we now need a struct device parent in the
> Scsi_Host or netdevice.  Every modern driver has these, but there might
> still be a few outdated legacy drivers out there, which now won't make
> an intelligent decision.
>
> Signed-off-by: Christoph Hellwig <hch@....de>

For m68k:
Acked-by: Geert Uytterhoeven <geert@...ux-m68k.org>

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

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