Subject: [RFC/PATCH 1/9] arm: dma-mapping: Don't override dma_ops in arch_setup_dma_ops()

From: [email-masked] (Will Deacon)
Date: Wed, 27 May 2015 18:38:06 +0100

On Fri, May 15, 2015 at 12:00:02AM +0100, Laurent Pinchart wrote:
> The arch_setup_dma_ops() function is in charge of setting dma_ops with a
> call to set_dma_ops(). set_dma_ops() is also called from
> 
> - highbank and mvebu bus notifiers
> - dmabounce (to be replaced with swiotlb)
> - arm_iommu_attach_device
> 
> (arm_iommu_attach_device is itself called from IOMMU and bus master
> device drivers)
> 
> To allow the arch_setup_dma_ops() call to be moved from device add time
> to device probe time we must ensure that dma_ops already setup by any of
> the above callers will not be overriden.
> 
> Aftering replacing dmabounce with swiotlb, converting IOMMU drivers to

s/Aftering/After/

> of_xlate and taking care of highbank and mvebu, the workaround should be
> removed.
> 
> Signed-off-by: Laurent Pinchart <[email-masked]>
> ---
>  arch/arm/mm/dma-mapping.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
> index 09c5fe3d30c2..7aa5e339a596 100644
> --- a/arch/arm/mm/dma-mapping.c
> +++ b/arch/arm/mm/dma-mapping.c
> @@ -2117,6 +2117,15 @@ void arch_setup_dma_ops(struct device *dev, u64 dma_base, u64 size,
>  	struct dma_map_ops *dma_ops;
>  
>  	dev->archdata.dma_coherent = coherent;
> +
> +	/*
> +	 * Don't override the dma_ops if they have already been set. Ideally
> +	 * this should be the only location where dma_ops are set, remove this
> +	 * check when all other callers of set_dma_ops will have disappeared.
> +	 */
> +	if (dev->archdata.dma_ops)
> +		return;

Maybe printing a warning at the same time will encourage people to migrate
away from the existing behaviour?

Will