Re: [PATCH 1/3] ARM/dma-mapping: move various helpers from dma-mapping.h to dma-direct.h

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

On 2020-09-10 06:40, Christoph Hellwig wrote:
> Move the helpers to translate to and from direct mapping DMA addresses
> to dma-direct.h.  This not only is the most logical place, but the new
> placement also avoids dependency loops with pending commits.

For the straightforward move as it should be,

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

However I do wonder how much of this could be cleaned up further...

> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>   arch/arm/common/dmabounce.c        |  2 +-
>   arch/arm/include/asm/dma-direct.h  | 70 ++++++++++++++++++++++++++++++
>   arch/arm/include/asm/dma-mapping.h | 70 ------------------------------
>   3 files changed, 71 insertions(+), 71 deletions(-)
> 
> diff --git a/arch/arm/common/dmabounce.c b/arch/arm/common/dmabounce.c
> index f4b719bde76367..d3e00ea9208834 100644
> --- a/arch/arm/common/dmabounce.c
> +++ b/arch/arm/common/dmabounce.c
> @@ -24,7 +24,7 @@
>   #include <linux/slab.h>
>   #include <linux/page-flags.h>
>   #include <linux/device.h>
> -#include <linux/dma-mapping.h>
> +#include <linux/dma-direct.h>
>   #include <linux/dmapool.h>
>   #include <linux/list.h>
>   #include <linux/scatterlist.h>
> diff --git a/arch/arm/include/asm/dma-direct.h b/arch/arm/include/asm/dma-direct.h
> index 7c3001a6a775bf..de0f4ff9279615 100644
> --- a/arch/arm/include/asm/dma-direct.h
> +++ b/arch/arm/include/asm/dma-direct.h
> @@ -2,6 +2,76 @@
>   #ifndef ASM_ARM_DMA_DIRECT_H
>   #define ASM_ARM_DMA_DIRECT_H 1
>   
> +#include <asm/memory.h>
> +
> +#ifdef __arch_page_to_dma
> +#error Please update to __arch_pfn_to_dma
> +#endif

This must be long, long dead by now.

> +
> +/*
> + * dma_to_pfn/pfn_to_dma/dma_to_virt/virt_to_dma are architecture private
> + * 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)
> +{
> +	if (dev)
> +		pfn -= dev->dma_pfn_offset;
> +	return (dma_addr_t)__pfn_to_bus(pfn);
> +}
> +
> +static inline unsigned long dma_to_pfn(struct device *dev, dma_addr_t addr)
> +{
> +	unsigned long pfn = __bus_to_pfn(addr);
> +
> +	if (dev)
> +		pfn += dev->dma_pfn_offset;
> +
> +	return pfn;
> +}

These are only overridden for OMAP1510, and it looks like it wouldn't 
take much for the platform code or ohci-omap driver to set up a generic 
DMA offset for the relevant device.

> +
> +static inline void *dma_to_virt(struct device *dev, dma_addr_t addr)
> +{
> +	if (dev) {
> +		unsigned long pfn = dma_to_pfn(dev, addr);
> +
> +		return phys_to_virt(__pfn_to_phys(pfn));
> +	}
> +
> +	return (void *)__bus_to_virt((unsigned long)addr);
> +}

This appears entirely unused.

> +
> +static inline dma_addr_t virt_to_dma(struct device *dev, void *addr)
> +{
> +	if (dev)
> +		return pfn_to_dma(dev, virt_to_pfn(addr));
> +
> +	return (dma_addr_t)__virt_to_bus((unsigned long)(addr));
> +}

And this is only used for some debug prints in dmabounce.

Similarly the __bus_to_*()/__*_to_bus() calls themselves only appear 
significant to mach-footbridge any more, and could probably also be 
evolved into regular DMA offsets now that all API calls must have a 
non-NULL device. I think I might come back and take a closer look at all 
this at some point in future... :)

Robin.

> +
> +#else
> +static inline dma_addr_t pfn_to_dma(struct device *dev, unsigned long pfn)
> +{
> +	return __arch_pfn_to_dma(dev, pfn);
> +}
> +
> +static inline unsigned long dma_to_pfn(struct device *dev, dma_addr_t addr)
> +{
> +	return __arch_dma_to_pfn(dev, addr);
> +}
> +
> +static inline void *dma_to_virt(struct device *dev, dma_addr_t addr)
> +{
> +	return __arch_dma_to_virt(dev, addr);
> +}
> +
> +static inline dma_addr_t virt_to_dma(struct device *dev, void *addr)
> +{
> +	return __arch_virt_to_dma(dev, addr);
> +}
> +#endif
> +
>   static inline dma_addr_t __phys_to_dma(struct device *dev, phys_addr_t paddr)
>   {
>   	unsigned int offset = paddr & ~PAGE_MASK;
> diff --git a/arch/arm/include/asm/dma-mapping.h b/arch/arm/include/asm/dma-mapping.h
> index bdd80ddbca3451..0a1a536368c3a4 100644
> --- a/arch/arm/include/asm/dma-mapping.h
> +++ b/arch/arm/include/asm/dma-mapping.h
> @@ -8,8 +8,6 @@
>   #include <linux/scatterlist.h>
>   #include <linux/dma-debug.h>
>   
> -#include <asm/memory.h>
> -
>   #include <xen/xen.h>
>   #include <asm/xen/hypervisor.h>
>   
> @@ -23,74 +21,6 @@ static inline const struct dma_map_ops *get_arch_dma_ops(struct bus_type *bus)
>   	return NULL;
>   }
>   
> -#ifdef __arch_page_to_dma
> -#error Please update to __arch_pfn_to_dma
> -#endif
> -
> -/*
> - * dma_to_pfn/pfn_to_dma/dma_to_virt/virt_to_dma are architecture private
> - * 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)
> -{
> -	if (dev)
> -		pfn -= dev->dma_pfn_offset;
> -	return (dma_addr_t)__pfn_to_bus(pfn);
> -}
> -
> -static inline unsigned long dma_to_pfn(struct device *dev, dma_addr_t addr)
> -{
> -	unsigned long pfn = __bus_to_pfn(addr);
> -
> -	if (dev)
> -		pfn += dev->dma_pfn_offset;
> -
> -	return pfn;
> -}
> -
> -static inline void *dma_to_virt(struct device *dev, dma_addr_t addr)
> -{
> -	if (dev) {
> -		unsigned long pfn = dma_to_pfn(dev, addr);
> -
> -		return phys_to_virt(__pfn_to_phys(pfn));
> -	}
> -
> -	return (void *)__bus_to_virt((unsigned long)addr);
> -}
> -
> -static inline dma_addr_t virt_to_dma(struct device *dev, void *addr)
> -{
> -	if (dev)
> -		return pfn_to_dma(dev, virt_to_pfn(addr));
> -
> -	return (dma_addr_t)__virt_to_bus((unsigned long)(addr));
> -}
> -
> -#else
> -static inline dma_addr_t pfn_to_dma(struct device *dev, unsigned long pfn)
> -{
> -	return __arch_pfn_to_dma(dev, pfn);
> -}
> -
> -static inline unsigned long dma_to_pfn(struct device *dev, dma_addr_t addr)
> -{
> -	return __arch_dma_to_pfn(dev, addr);
> -}
> -
> -static inline void *dma_to_virt(struct device *dev, dma_addr_t addr)
> -{
> -	return __arch_dma_to_virt(dev, addr);
> -}
> -
> -static inline dma_addr_t virt_to_dma(struct device *dev, void *addr)
> -{
> -	return __arch_virt_to_dma(dev, addr);
> -}
> -#endif
> -
>   /**
>    * arm_dma_alloc - allocate consistent memory for DMA
>    * @dev: valid struct device pointer, or NULL for ISA and EISA-like devices
> 
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