[U-Boot] [RFC PATCH] ARM: asm: types: Introduce DMA_ADDR_T_64BIT

[Lukasz Majewski]

Hi Lokesh,

> dma_addr_t holds any valid DMA address. If the DMA API only uses
> 32-bit addresses, dma_addr_t need only be 32 bits wide.  Bus
> addresses, e.g., PCI BARs, may be wider than 32 bits, but drivers do
> memory-mapped I/O to ioremapped kernel virtual addresses, so they
> don't care about the size of the actual bus addresses.
> Also 32 bit ARM systems with LPAE enabled can use 64bit address
> space, but DMA still use 32bit address like in case of DRA7 and
> Keystone platforms.

I've already stumbled upon this issue...

> 
> This is inspired from the Linux kernel types implementation[1]
> 
> [1]
> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/include/linux/types.h#n142
> 
> Signed-off-by: Lokesh Vutla <lokeshvutla at ti.com>
> ---
>  arch/arm/include/asm/types.h | 17 +++++++++++++++--
>  1 file changed, 15 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm/include/asm/types.h
> b/arch/arm/include/asm/types.h index 388058e..d108915 100644
> --- a/arch/arm/include/asm/types.h
> +++ b/arch/arm/include/asm/types.h
> @@ -46,16 +46,29 @@ typedef unsigned long long u64;
>  #endif	/* CONFIG_ARM64 */
>  
>  #ifdef CONFIG_PHYS_64BIT
> -typedef unsigned long long dma_addr_t;
>  typedef unsigned long long phys_addr_t;
>  typedef unsigned long long phys_size_t;
>  #else
>  /* DMA addresses are 32-bits wide */
> -typedef u32 dma_addr_t;
>  typedef unsigned long phys_addr_t;
>  typedef unsigned long phys_size_t;
>  #endif
>  
> +/*
> + * A dma_addr_t can hold any valid DMA address, i.e., any address
> returned
> + * by the DMA API.
> + *
> + * If the DMA API only uses 32-bit addresses, dma_addr_t need only
> be 32
> + * bits wide.  Bus addresses, e.g., PCI BARs, may be wider than 32
> bits,
> + * but drivers do memory-mapped I/O to ioremapped kernel virtual
> addresses,
> + * so they don't care about the size of the actual bus addresses.
> + */
> +#ifdef CONFIG_DMA_ADDR_T_64BIT

Generally this approach is correct, but please pay attention to the
CONFIG_PHYS_64BIT.

The actual size of dma_addr_t (64 or 32 bits) is decided by defining or
undefining CONFIG_PHYS_64BIT at arch/arm/include/asm/config.h. This is
based on the status of CONFIG_ARM64.

To avoid regression we need to take into account status of CONFIG_ARM64
to be sure that CONFIG_DMA_ADDR_T_64BIT is set on ARM64 systems.

> +typedef unsigned long long dma_addr_t;
> +#else
> +typedef u32 dma_addr_t;
> +#endif
> +
>  #endif /* __KERNEL__ */
>  
>  typedef unsigned long resource_size_t;



-- 
Best regards,

Lukasz Majewski

Samsung R&D Institute Poland (SRPOL) | Linux Platform Group