Re: [RFC PATCH v4 8/8] arm: dma-mapping: plumb our iommu mapping ops into arch_setup_dma_ops

[Robin Murphy <robin.murphy@arm.com>]

Hi Will,

On 14/11/14 18:56, Will Deacon wrote:
> This patch plumbs the existing ARM IOMMU DMA infrastructure (which isn't
> actually called outside of a few drivers) into arch_setup_dma_ops, so
> that we can use IOMMUs for DMA transfers in a more generic fashion.
>
> Since this significantly complicates the arch_setup_dma_ops function,
> it is moved out of line into dma-mapping.c. If CONFIG_ARM_DMA_USE_IOMMU
> is not set, the iommu parameter is ignored and the normal ops are used
> instead.
>
> Signed-off-by: Will Deacon <will.deacon@arm.com>

[...]

> +static bool arm_setup_iommu_dma_ops(struct device *dev, u64 dma_base, u64 size,
> +				    struct iommu_ops *iommu)
> +{
> +	struct dma_iommu_mapping *mapping;
> +
> +	mapping = arm_iommu_create_mapping(dev->bus, dma_base, size);
> +	if (IS_ERR(mapping)) {
> +		pr_warn("Failed to create %llu-byte IOMMU mapping for device %s\n",
> +				size, dev_name(dev));
> +		return false;
> +	}
> +
> +	if (arm_iommu_attach_device(dev, mapping)) {
> +		pr_warn("Failed to attached device %s to IOMMU_mapping\n",
> +				dev_name(dev));
> +		arm_iommu_release_mapping(mapping);
> +		return false;
> +	}
> +
> +	return true;
> +}
> +
> +static void arm_teardown_iommu_dma_ops(struct device *dev)
> +{
> +	struct dma_iommu_mapping *mapping = dev->archdata.mapping;
> +
> +	arm_iommu_detach_device(dev);
> +	arm_iommu_release_mapping(mapping);
> +}
> +
> +#else
> +
> +static bool arm_setup_iommu_dma_ops(struct device *dev, u64 dma_base, u64 size,
> +				    struct iommu_ops *iommu)
> +{
> +	return false;
> +}
> +
> +static void arm_teardown_iommu_dma_ops(struct device *dev) { }
> +
> +#define arm_get_iommu_dma_map_ops arm_get_dma_map_ops
> +
> +#endif	/* CONFIG_ARM_DMA_USE_IOMMU */
> +
> +static struct dma_map_ops *arm_get_dma_map_ops(bool coherent)
> +{
> +	return coherent ? &arm_coherent_dma_ops : &arm_dma_ops;
> +}
> +
> +void arch_setup_dma_ops(struct device *dev, u64 dma_base, u64 size,
> +			struct iommu_ops *iommu, bool coherent)
> +{
> +	struct dma_map_ops *dma_ops;
> +
> +	if (arm_setup_iommu_dma_ops(dev, dma_base, size, iommu))

Is the loss of a null check on iommu (compared to previous versions) 
intentional? It looks like you're always going to call 
arm_setup_iommu_dma_ops here for everything regardless, and given that 
that doesn't even look at the iommu parameter, relying on it to somehow 
fail correctly smells a bit off.


Robin.

> +		dma_ops = arm_get_iommu_dma_map_ops(coherent);
> +	else
> +		dma_ops = arm_get_dma_map_ops(coherent);
> +
> +	set_dma_ops(dev, dma_ops);
> +}
> +
> +void arch_teardown_dma_ops(struct device *dev)
> +{
> +	arm_teardown_iommu_dma_ops(dev);
> +}
>