Re: [PATCH] MIPS: Use CPHYSADDR to implement mips32 __pa

[Matt Redfearn <matt.redfearn@imgtec.com>]

Hi Paul,

On 14/02/16 19:20, Paul Burton wrote:
> Use CPHYSADDR to implement the __pa macro converting from a virtual to a
> physical address for MIPS32, much as is already done for MIPS64 (though
> without the complication of having both compatibility & XKPHYS
> segments).
>
> This allows for __pa to work regardless of whether the address being
> translated is in kseg0 or kseg1, unlike the previous subtraction based
> approach which only worked for addresses in kseg0. Working for kseg1
> addresses is important if __pa is used on addresses allocated by
> dma_alloc_coherent, where on systems with non-coherent I/O we provide
> addresses in kseg1. If this address is then used with
> dma_map_single_attrs then it is provided to virt_to_page, which in turn
> calls virt_to_phys which is a wrapper around __pa. The result is that we
> end up with a physical address 0x20000000 bytes (ie. the size of kseg0)
> too high.
>
> In addition to providing consistency with MIPS64 & fixing the kseg1 case
> above this has the added bonus of generating smaller code for systems
> implementing MIPS32r2 & beyond, where a single ext instruction can
> extract the physical address rather than needing to load an immediate
> into a temp register & subtract it. This results in ~1.3KB savings for a
> boston_defconfig kernel adjusted to set CONFIG_32BIT=y.
>
> Signed-off-by: Paul Burton <paul.burton@imgtec.com>
> ---
>
>   arch/mips/include/asm/page.h | 3 +--
>   1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/arch/mips/include/asm/page.h b/arch/mips/include/asm/page.h
> index 21ed715..35c1222 100644
> --- a/arch/mips/include/asm/page.h
> +++ b/arch/mips/include/asm/page.h
> @@ -169,8 +169,7 @@ typedef struct { unsigned long pgprot; } pgprot_t;
>       __x < CKSEG0 ? XPHYSADDR(__x) : CPHYSADDR(__x);			\
>   })
>   #else
> -#define __pa(x)								\
> -    ((unsigned long)(x) - PAGE_OFFSET + PHYS_OFFSET)
> +#define __pa(x)		CPHYSADDR(x)
>   #endif
>   #define __va(x)		((void *)((unsigned long)(x) + PAGE_OFFSET - PHYS_OFFSET))
>   #include <asm/io.h>
I have tested this patch on an EVA Interaptiv and confirmed that it 
fixes previous regressions.

Tested-by: Matt Redfearn <matt.redfearn@imgtec.com>

Thanks,
Matt