Subject: Re: [PATCH] dma/direct: turn ARCH_ZONE_DMA_BITS into a variable

From: Christoph Hellwig <[email-masked]>
Date: Thu, 31 Oct 2019 16:47:59 +0100

On Thu, Oct 31, 2019 at 04:28:37PM +0100, Nicolas Saenz Julienne wrote:
> Some architectures, notably ARM, are interested in tweaking this
> depending on their runtime DMA addressing limitations.
> 
> Signed-off-by: Nicolas Saenz Julienne <[email-masked]>
> ---
> 
> Changes since RFC:
>  - Rebased to v5.4-rc6, fixed arm64 code.
> 
> NOTE: This will only apply to linux-next, where 

missing end of the sentence.  But only applying to linux-next isn't
going to help anyone..

> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> index 45c00a54909c..f716ea634804 100644
> --- a/arch/arm64/mm/init.c
> +++ b/arch/arm64/mm/init.c
> @@ -20,6 +20,7 @@
>  #include <linux/sort.h>
>  #include <linux/of.h>
>  #include <linux/of_fdt.h>
> +#include <linux/dma-direct.h>
>  #include <linux/dma-mapping.h>
>  #include <linux/dma-contiguous.h>
>  #include <linux/efi.h>
> @@ -41,6 +42,8 @@
>  #include <asm/tlb.h>
>  #include <asm/alternative.h>
>  
> +#define ARM64_ZONE_DMA_BITS	30
> +
>  /*
>   * We need to be able to catch inadvertent references to memstart_addr
>   * that occur (potentially in generic code) before arm64_memblock_init()
> @@ -424,6 +427,8 @@ void __init arm64_memblock_init(void)
>  	else
>  		arm64_dma_phys_limit = PHYS_MASK + 1;
>  
> +	zone_dma_bits = ARM64_ZONE_DMA_BITS;
> +
>  	reserve_crashkernel();

This actually adds a new limit, as there wasn't one before for arm64.

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