linux-kernel - Re: [PATCH 21/44] powerpc: implement ->mapping

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Date:   Wed, 14 Jun 2017 19:17:27 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Christoph Hellwig <hch@....de>, x86@...nel.org,
        linux-arm-kernel@...ts.infradead.org,
        xen-devel@...ts.xenproject.org, linux-c6x-dev@...ux-c6x.org,
        linux-hexagon@...r.kernel.org, linux-ia64@...r.kernel.org,
        linux-mips@...ux-mips.org, openrisc@...ts.librecores.org,
        linuxppc-dev@...ts.ozlabs.org, linux-s390@...r.kernel.org,
        linux-sh@...r.kernel.org, sparclinux@...r.kernel.org,
        linux-xtensa@...ux-xtensa.org, dmaengine@...r.kernel.org,
        linux-tegra@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-samsung-soc@...r.kernel.org,
        iommu@...ts.linux-foundation.org, netdev@...r.kernel.org,
        Alistair Popple <apopple@....ibm.com>
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH 21/44] powerpc: implement ->mapping_error

Christoph Hellwig <hch@....de> writes:

> DMA_ERROR_CODE is going to go away, so don't rely on it.  Instead
> define a ->mapping_error method for all IOMMU based dma operation
> instances.  The direct ops don't ever return an error and don't
> need a ->mapping_error method.
>
> Signed-off-by: Christoph Hellwig <hch@....de>
> ---
>  arch/powerpc/include/asm/dma-mapping.h |  4 ----
>  arch/powerpc/include/asm/iommu.h       |  4 ++++
>  arch/powerpc/kernel/dma-iommu.c        |  6 ++++++
>  arch/powerpc/kernel/iommu.c            | 28 ++++++++++++++--------------
>  arch/powerpc/platforms/cell/iommu.c    |  1 +
>  arch/powerpc/platforms/pseries/vio.c   |  3 ++-
>  6 files changed, 27 insertions(+), 19 deletions(-)

I also see:

  arch/powerpc/kernel/dma.c:const struct dma_map_ops dma_direct_ops = {

Which you mentioned can't fail.

  arch/powerpc/platforms/pseries/ibmebus.c:static const struct dma_map_ops ibmebus_dma_ops = {

Which can't fail.

And:

  arch/powerpc/platforms/powernv/npu-dma.c:static const struct dma_map_ops dma_npu_ops = {
  arch/powerpc/platforms/ps3/system-bus.c:static const struct dma_map_ops ps3_sb_dma_ops = {
  arch/powerpc/platforms/ps3/system-bus.c:static const struct dma_map_ops ps3_ioc0_dma_ops = {

All of which look like they definitely can fail, but return 0 on error
and don't implement ->mapping_error.

So I guess I'm acking this and adding a TODO to fix up the NPU code at
least, the ps3 code is probably better left alone these days.

Acked-by: Michael Ellerman <mpe@...erman.id.au>

cheers