Re: [RFC PATCH v3 5/7] dma-mapping: detect and configure IOMMU in of_dma_configure

[Laurent Pinchart <laurent.pinchart-ryLnwIuWjnjg/C1BVhZhaw@public.gmane.org>]

Hi Will,

Thank you for the patch.

On Friday 12 September 2014 17:34:53 Will Deacon wrote:
> This patch extends of_dma_configure so that it sets up the IOMMU for a
> device, as well as the coherent/non-coherent DMA mapping ops.
> 
> Signed-off-by: Will Deacon <will.deacon-5wv7dgnIgG8@public.gmane.org>
> ---
>  arch/arm/include/asm/dma-mapping.h |  4 +++-
>  drivers/of/platform.c              | 24 +++++++++++++++++-------
>  include/linux/dma-mapping.h        |  8 +++++++-
>  3 files changed, 27 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/arm/include/asm/dma-mapping.h
> b/arch/arm/include/asm/dma-mapping.h index 7e9ac4f604c3..a8bb0c494bb3
> 100644
> --- a/arch/arm/include/asm/dma-mapping.h
> +++ b/arch/arm/include/asm/dma-mapping.h
> @@ -121,7 +121,9 @@ static inline unsigned long dma_max_pfn(struct device
> *dev) }
>  #define dma_max_pfn(dev) dma_max_pfn(dev)
> 
> -static inline void arch_setup_dma_ops(struct device *dev, bool coherent)
> +static inline void arch_setup_dma_ops(struct device *dev, u64 dma_base,
> +				      u64 size, struct iommu_dma_mapping *iommu,
> +				      bool coherent)
>  {
>  	if (coherent)
>  		set_dma_ops(dev, &arm_coherent_dma_ops);
> diff --git a/drivers/of/platform.c b/drivers/of/platform.c
> index 946dd7ae0394..95ebd38db545 100644
> --- a/drivers/of/platform.c
> +++ b/drivers/of/platform.c
> @@ -19,6 +19,7 @@
>  #include <linux/slab.h>
>  #include <linux/of_address.h>
>  #include <linux/of_device.h>
> +#include <linux/of_iommu.h>
>  #include <linux/of_irq.h>
>  #include <linux/of_platform.h>
>  #include <linux/platform_device.h>
> @@ -166,6 +167,7 @@ static void of_dma_configure(struct platform_device
> *pdev) int ret;
>  	bool coherent;
>  	unsigned long offset;
> +	struct iommu_dma_mapping *iommu;
>  	struct device *dev = &pdev->dev;
> 
>  	/*
> @@ -195,7 +197,19 @@ static void of_dma_configure(struct platform_device
> *pdev) dev_dbg(dev, "device is%sdma coherent\n",
>  		coherent ? " " : " not ");
> 
> -	arch_setup_dma_ops(dev, coherent);
> +	iommu = of_iommu_configure(dev);
> +	dev_dbg(dev, "device is%sbehind an iommu\n",
> +		iommu ? " " : " not ");
> +
> +	arch_setup_dma_ops(dev, dma_addr, size, iommu, coherent);
> +
> +	if (iommu)
> +		kref_put(&iommu->kref, of_iommu_deconfigure);

What's the expected life cycle of the iommu_dma_mapping structure ? It gets 
created by of_iommu_configure() and the initial reference gets dropped here. I 
suppose you expect arch code to need to keep a reference to the structure, but 
your implementation in patch 7/7 doesn't. As far as I can see, you don't even 
use the contents of the structure in the ARM arch_setup_dma_ops() 
implementation. Do you expect that to change later, or other architectures to 
need it ?

By the way, now that I think about it, I find struct iommu_dma_mapping and 
struct dma_iommu_mapping very confusing.

> +}
> +
> +static void of_dma_deconfigure(struct platform_device *pdev)
> +{
> +	arch_teardown_dma_ops(&pdev->dev);
>  }
> 
>  /**
> @@ -224,16 +238,12 @@ static struct platform_device
> *of_platform_device_create_pdata( if (!dev)
>  		goto err_clear_flag;
> 
> -	of_dma_configure(dev);
>  	dev->dev.bus = &platform_bus_type;
>  	dev->dev.platform_data = platform_data;
> -
> -	/* We do not fill the DMA ops for platform devices by default.
> -	 * This is currently the responsibility of the platform code
> -	 * to do such, possibly using a device notifier
> -	 */
> +	of_dma_configure(dev);
> 
>  	if (of_device_add(dev) != 0) {
> +		of_dma_deconfigure(dev);
>  		platform_device_put(dev);
>  		goto err_clear_flag;
>  	}
> diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
> index e60e52d82db9..47e1ac30e300 100644
> --- a/include/linux/dma-mapping.h
> +++ b/include/linux/dma-mapping.h
> @@ -138,7 +138,13 @@ static inline int dma_coerce_mask_and_coherent(struct
> device *dev, u64 mask) extern u64 dma_get_required_mask(struct device
> *dev);
> 
>  #ifndef arch_setup_dma_ops
> -static inline void arch_setup_dma_ops(struct device *dev, bool coherent) {
> } +static inline void arch_setup_dma_ops(struct device *dev, u64 dma_base,
> +				      u64 size, struct iommu_dma_mapping *iommu,
> +				      bool coherent) { }
> +#endif
> +
> +#ifndef arch_teardown_dma_ops
> +static inline void arch_teardown_dma_ops(struct device *dev) { }
>  #endif
> 
>  static inline unsigned int dma_get_max_seg_size(struct device *dev)

-- 
Regards,

Laurent Pinchart