Re: [PATCH] MIPS: mm: Move some checks out of 'for' loop in DMA operations

["Jayachandran C." <jchandra@broadcom.com>]

On Wed, Sep 25, 2013 at 06:31:05PM +0530, Jayachandran C wrote:

The patch was missing the required Signed-off-by, added below.

> The check cpu_needs_post_dma_flush() in mips_dma_sync_sg_for_cpu() and
> the check !plat_device_is_coherent() in mips_dma_sync_sg_for_device()
> can be moved outside the for loop.
> 
> As a side effect, this also avoids a GCC bug that caused kernel compile
> to fail with the error:
> 
> arch/mips/mm/dma-default.c: In function 'mips_dma_sync_sg_for_cpu':
> arch/mips/mm/dma-default.c:316:1: internal compiler error: in add_insn_before, at emit-rtl.c:3852
> 
> This gcc failure is seen in Code Sourcery toolchains [e.g. gcc version
> 4.7.2 (Sourcery CodeBench Lite 2012.09-99)] after commit "MIPS: Optimize
> current_cpu_type() for better code."

Signed-off-by: Jayachandran C <jchandra@broadcom.com>

> ---
>  arch/mips/mm/dma-default.c |   12 ++++--------
>  1 file changed, 4 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/mips/mm/dma-default.c b/arch/mips/mm/dma-default.c
> index e45e4b0..2e94185 100644
> --- a/arch/mips/mm/dma-default.c
> +++ b/arch/mips/mm/dma-default.c
> @@ -307,12 +307,10 @@ static void mips_dma_sync_sg_for_cpu(struct device *dev,
>  {
>  	int i;
>  
> -	/* Make sure that gcc doesn't leave the empty loop body.  */
> -	for (i = 0; i < nelems; i++, sg++) {
> -		if (cpu_needs_post_dma_flush(dev))
> +	if (cpu_needs_post_dma_flush(dev))
> +		for (i = 0; i < nelems; i++, sg++)
>  			__dma_sync(sg_page(sg), sg->offset, sg->length,
>  				   direction);
> -	}
>  }
>  
>  static void mips_dma_sync_sg_for_device(struct device *dev,
> @@ -320,12 +318,10 @@ static void mips_dma_sync_sg_for_device(struct device *dev,
>  {
>  	int i;
>  
> -	/* Make sure that gcc doesn't leave the empty loop body.  */
> -	for (i = 0; i < nelems; i++, sg++) {
> -		if (!plat_device_is_coherent(dev))
> +	if (!plat_device_is_coherent(dev))
> +		for (i = 0; i < nelems; i++, sg++)
>  			__dma_sync(sg_page(sg), sg->offset, sg->length,
>  				   direction);
> -	}
>  }
>  
>  int mips_dma_mapping_error(struct device *dev, dma_addr_t dma_addr)

JC.