[RFC/RFT 1/2] ARM: mm: introduce arch hooks for dma address translation routines

[Olof Johansson]

Hi,


On Mon, Feb 3, 2014 at 3:28 PM, Santosh Shilimkar
<santosh.shilimkar at ti.com> wrote:
> Currently arch specific DMA address translation routines can be enabled
> using only defines which makes impossible to use them in with
> multi-platform builds.
>
> Hence, introduce arch specific hooks for DMA address translations
> routines to be compatible with multi-platform builds:
> dma_addr_t (*arch_pfn_to_dma)(struct device *dev, unsigned long pfn);
> unsigned long (*arch_dma_to_pfn)(struct device *dev, dma_addr_t addr);
> void* (*arch_dma_to_virt)(struct device *dev, dma_addr_t addr);
> dma_addr_t (*arch_virt_to_dma)(struct device *dev, void *addr);
>
> In case if architecture won't use it - DMA address translation routines
> will fall-back to existing implementation.
>
> Also, modify machines omap1, ks8695, iop13xx to use new DMA hooks.

[...]

> diff --git a/arch/arm/include/asm/dma-mapping.h b/arch/arm/include/asm/dma-mapping.h
> index e701a4d..84acc46 100644
> --- a/arch/arm/include/asm/dma-mapping.h
> +++ b/arch/arm/include/asm/dma-mapping.h
> @@ -55,28 +55,16 @@ static inline int dma_set_mask(struct device *dev, u64 mask)
>   * functions used internally by the DMA-mapping API to provide DMA
>   * addresses. They must not be used by drivers.
>   */
> -#ifndef __arch_pfn_to_dma
> -static inline dma_addr_t pfn_to_dma(struct device *dev, unsigned long pfn)
> -{
> -       return (dma_addr_t)__pfn_to_bus(pfn);
> -}
>
> -static inline unsigned long dma_to_pfn(struct device *dev, dma_addr_t addr)
> -{
> -       return __bus_to_pfn(addr);
> -}
> +extern dma_addr_t (*__arch_pfn_to_dma)(struct device *dev, unsigned long pfn);
> +extern unsigned long (*__arch_dma_to_pfn)(struct device *dev, dma_addr_t addr);
> +extern void* (*__arch_dma_to_virt)(struct device *dev, dma_addr_t addr);
> +extern dma_addr_t (*__arch_virt_to_dma)(struct device *dev, void *addr);

I tend to prefer having these kind of function pointers grouped in a
struct instead of in the toplevel namespace like this. It allows you
to use a set_<foo>_ops() interface too instead and reduces
exposed/exported internals since only the global struct pointer has to
be exported.

>
> -static inline void *dma_to_virt(struct device *dev, dma_addr_t addr)
> -{
> -       return (void *)__bus_to_virt((unsigned long)addr);
> -}

I don't actually see any in-tree users of dma_to_virt(). It can
probably be removed.

> -static inline dma_addr_t virt_to_dma(struct device *dev, void *addr)
> -{
> -       return (dma_addr_t)__virt_to_bus((unsigned long)(addr));
> -}
> +/* Keep __arch_pfn_to_dma defined as it's used by some drivers (V4L2)*/
> +#define __arch_pfn_to_dma __arch_pfn_to_dma

Ick. The v4l driver should be fixed. Marek?


[...]

> diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
> index 5c43ca5..74111bf 100644
> --- a/arch/arm/mm/dma-mapping.c
> +++ b/arch/arm/mm/dma-mapping.c
> @@ -39,6 +39,35 @@
>
>  #include "mm.h"
>
> +static inline dma_addr_t __pfn_to_dma(struct device *dev, unsigned long pfn)
> +{
> +       return (dma_addr_t)__pfn_to_bus(pfn);
> +}
> +
> +static inline unsigned long __dma_to_pfn(struct device *dev, dma_addr_t addr)
> +{
> +       return __bus_to_pfn(addr);
> +}
> +
> +static inline void *__dma_to_virt(struct device *dev, dma_addr_t addr)
> +{
> +       return (void *)__bus_to_virt((unsigned long)addr);
> +}
> +
> +static inline dma_addr_t __virt_to_dma(struct device *dev, void *addr)
> +{
> +       return (dma_addr_t)__virt_to_bus((unsigned long)(addr));
> +}
> +
> +dma_addr_t (*__arch_pfn_to_dma)(struct device *dev, unsigned long pfn) = __pfn_to_dma;
> +EXPORT_SYMBOL(__arch_pfn_to_dma);
> +unsigned long (*__arch_dma_to_pfn)(struct device *dev, dma_addr_t addr) = __dma_to_pfn;
> +EXPORT_SYMBOL(__arch_dma_to_pfn);
> +void* (*__arch_dma_to_virt)(struct device *dev, dma_addr_t addr) = __dma_to_virt;
> +EXPORT_SYMBOL(__arch_dma_to_virt);
> +dma_addr_t (*__arch_virt_to_dma)(struct device *dev, void *addr) = __virt_to_dma;
> +EXPORT_SYMBOL(__arch_virt_to_dma);

Independent on whether someone objects to my preference of exporting a
struct, these (or that struct pointer) should probably be
EXPORT_SYMBOL_GPL().


-Olof