linux-kernel - Re: [PATCH 04/12] dma-mapping: fix DMA

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Date:   Thu, 10 Sep 2020 13:55:37 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Christoph Hellwig <hch@....de>, Tony Luck <tony.luck@...el.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        iommu@...ts.linux-foundation.org
Cc:     Tomasz Figa <tfiga@...omium.org>, Joerg Roedel <joro@...tes.org>,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-ia64@...r.kernel.org, linux-mips@...r.kernel.org
Subject: Re: [PATCH 04/12] dma-mapping: fix DMA_OPS dependencies

On 2020-09-08 17:47, Christoph Hellwig wrote:
> Driver that select DMA_OPS need to depend on HAS_DMA support to
> work.  The vop driver was missing that dependency, so add it, and also
> add a nother depends in DMA_OPS itself.  That won't fix the issue due
> to how the Kconfig dependencies work, but at least produce a warning
> about unmet dependencies.
> 
> Signed-off-by: Christoph Hellwig <hch@....de>
> ---
>   drivers/misc/mic/Kconfig | 1 +
>   kernel/dma/Kconfig       | 1 +
>   2 files changed, 2 insertions(+)
> 
> diff --git a/drivers/misc/mic/Kconfig b/drivers/misc/mic/Kconfig
> index b9bb086785db48..8a7c2c5711d5f4 100644
> --- a/drivers/misc/mic/Kconfig
> +++ b/drivers/misc/mic/Kconfig
> @@ -35,6 +35,7 @@ config SCIF_BUS
>   
>   config VOP_BUS
>   	tristate "VOP Bus Driver"
> +	depends on HAS_DMA
>   	select DMA_OPS

AFAICS all three of these bus drivers are only proxying a struct 
dma_map_ops * pointer around, so if they used the set_dma_ops() helper 
they shouldn't even need these selects at all. Only INTEL_MIC_HOST 
appears to have a logical dependency on DMA_OPS for actual functionality.

However, I have a vague feeling you might not be fond of those dma_ops 
helpers, and I have no great objection to this one-liner as-is, so 
(modulo the couple of commit message typos),

Reviewed-by: Robin Murphy <robin.murphy@....com>

(of course the hunk below is unquestionably OK)

Robin.

>   	help
>   	  This option is selected by any driver which registers a
> diff --git a/kernel/dma/Kconfig b/kernel/dma/Kconfig
> index 0ddfb5510fe45f..e7b801649f6574 100644
> --- a/kernel/dma/Kconfig
> +++ b/kernel/dma/Kconfig
> @@ -9,6 +9,7 @@ config HAS_DMA
>   	default y
>   
>   config DMA_OPS
> +	depends on HAS_DMA
>   	bool
>   
>   #
>