Re: [PATCH] MIPS: dma-default: Fix 32-bit fall back to GFP_DMA

[Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>]

Hello.

On 03/26/2015 07:56 PM, James Hogan wrote:

> If there is a DMA zone (usually 24bit = 16MB I believe), but no DMA32
> zone, as is the case for some 32-bit kernels, then massage_gfp_flags()
> will cause DMA memory allocated for devices with a 32..63-bit
> coherent_dma_mask to fall back to using __GFP_DMA, even though there may
> only be 32-bits of physical address available anyway.

> Correct that case to compare against a mask the size of phys_addr_t
> instead of always using a 64-bit mask.

> Fixes: a2e715a86c6d ("MIPS: DMA: Fix computation of DMA flags from device's coherent_dma_mask.")
> Signed-off-by: James Hogan <james.hogan@imgtec.com>
> Cc: Ralf Baechle <ralf@linux-mips.org>
> Cc: linux-mips@linux-mips.org
> Cc: <stable@vger.kernel.org> # 2.6.36+
> ---
> This works around problems encountered on Malta with ethernet and IDE
> drivers being unable to allocate any coherent memory when the entire
> 16MB DMA zone is taken up with static kernel data (a separate problem),
> even though their coherent_dma_masks are 32-bit. This can happen when
> PROVE_RCU and PROVE_LOCKING are set, especially since commit
> 1413c0389333 ("lockdep: Increase static allocations") was applied in
> v3.16.
> ---
>   arch/mips/mm/dma-default.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)

> diff --git a/arch/mips/mm/dma-default.c b/arch/mips/mm/dma-default.c
> index af5f046e627e..501557026768 100644
> --- a/arch/mips/mm/dma-default.c
> +++ b/arch/mips/mm/dma-default.c
> @@ -100,7 +100,7 @@ static gfp_t massage_gfp_flags(const struct device *dev, gfp_t gfp)
>   	else
>   #endif
>   #if defined(CONFIG_ZONE_DMA) && !defined(CONFIG_ZONE_DMA32)
> -	     if (dev->coherent_dma_mask < DMA_BIT_MASK(64))
> +	     if (dev->coherent_dma_mask < DMA_BIT_MASK(sizeof(phys_addr_t)*8))

    Cold you add spaces around *, just to be consisted with the other binary 
operators? This seems a preferred kernel style anyway.

WBR, Sergei