linux-kernel - Re: [PATCH] MIPS: remove mips_swiotlb

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Message-ID: <20180728190618.sq5xbuc2hnthmkhl@pburton-laptop>
Date:   Sat, 28 Jul 2018 12:06:18 -0700
From:   Paul Burton <paul.burton@...s.com>
To:     Christoph Hellwig <hch@....de>
Cc:     David Daney <ddaney@...iumnetworks.com>,
        Huacai Chen <chenhc@...ote.com>, linux-mips@...ux-mips.org,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] MIPS: remove mips_swiotlb_ops

Hi Christoph,

On Fri, Jul 27, 2018 at 07:26:06PM +0200, Christoph Hellwig wrote:
> mips_swiotlb_ops differs from the generic swiotlb_dma_ops only in that
> it contains a mb() barrier after each operations that maps or syncs
> dma memory to the device.
> 
> The dma operations are defined to not be memory barriers, but instead
> the write* operations to kick the DMA off are supposed to contain them.
> 
> For mips this handled by war_io_reorder_wmb(), which evaluates to the
> stronger wmb() instead of the pure compiler barrier barrier() for
> just those platforms that use swiotlb, so I think we are covered
> properly.
> 
> Signed-off-by: Christoph Hellwig <hch@....de>
> ---
>  arch/mips/include/asm/dma-mapping.h |  3 +-
>  arch/mips/mm/Makefile               |  1 -
>  arch/mips/mm/dma-swiotlb.c          | 61 -----------------------------
>  3 files changed, 1 insertion(+), 64 deletions(-)
>  delete mode 100644 arch/mips/mm/dma-swiotlb.c

Thanks - this looks reasonable, but needed a small tweak to gain the
definition of swiotlb_dma_ops from linux/swiotlb.h (as riscv & unicore32
do) in order to avoid build failures.

Hooray for even more deleted code :)

Applied to mips-next for 4.19.

Paul