netdev - Re: [PATCH/RFC] dma-mapping: Provide dummy set_dma_ops() for NO

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Date:   Mon, 10 Jul 2017 09:55:27 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Christoph Hellwig <hch@....de>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>,
        Madalin Bucur <madalin.bucur@....com>,
        "David S . Miller" <davem@...emloft.net>,
        Networking <netdev@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH/RFC] dma-mapping: Provide dummy set_dma_ops() for NO_DMA=y

On Sun, Jul 9, 2017 at 9:33 PM, Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
> Adding a dummy for set_dma_ops() allows to compile (sub)drivers that
> don't actually use the DMA API, but propagate DMA ops configuration to a
> second driver that may or may not use the DMA API.  Of course the second
> driver does have to depend on HAS_DMA if it uses the DMA API.
>
> An example is commit 5567e989198b5a8d ("fsl/fman: propagate dma_ops").
>
> This allows to revert commit 85688d9adf685572 ("fsl/fman: add dependency
> on HAS_DMA").
>
> Signed-off-by: Geert Uytterhoeven <geert@...ux-m68k.org>

I can't think of any correct use case for this new helper. IMO a device
driver should never set the dma_map_ops for any device, and we should
instead for the fman driver correctly.

       Arnd