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Date:   Sat, 26 Dec 2020 11:35:58 +0100
From:   Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
To:     Chen Zhou <chenzhou10@...wei.com>, catalin.marinas@....com,
        will@...nel.org
Cc:     ardb@...nel.org, akpm@...ux-foundation.org, rppt@...nel.org,
        song.bao.hua@...ilicon.com, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, huawei.libin@...wei.com,
        xiexiuqi@...wei.com
Subject: Re: [PATCH 1/2] arm64: mm: update the comments about ZONE_DMA

On Sat, 2020-12-26 at 11:35 +0800, Chen Zhou wrote:
> Since patchset "arm64: Default to 32-bit wide ZONE_DMA", ZONE_DMA's
> size is fine-tuned. In the absence of addressing limited masters,
> ZONE_DMA will span the whole 32-bit address space, otherwise, in
> the case of the Raspberry Pi 4, it'll only span the 30-bit address
> space. Update the comments.
> 
> Signed-off-by: Chen Zhou <chenzhou10@...wei.com>
> ---

Reviewed-by: Nicolas Saenz Julienne <nsaenzjulienne@...e.de>

>  arch/arm64/mm/init.c | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> index 75addb36354a..7b9809e39927 100644
> --- a/arch/arm64/mm/init.c
> +++ b/arch/arm64/mm/init.c
> @@ -53,10 +53,11 @@ s64 memstart_addr __ro_after_init = -1;
>  EXPORT_SYMBOL(memstart_addr);
>  
> 
>  /*
> - * We create both ZONE_DMA and ZONE_DMA32. ZONE_DMA covers the first 1G of
> - * memory as some devices, namely the Raspberry Pi 4, have peripherals with
> - * this limited view of the memory. ZONE_DMA32 will cover the rest of the 32
> - * bit addressable memory area.
> + * We create both ZONE_DMA and ZONE_DMA32. ZONE_DMA's size is fine-tuned.
> + * In the absence of addressing limited masters, ZONE_DMA will span the
> + * whole 32-bit address space, otherwise, in the case of the Raspberry Pi 4,
> + * it'll only span the 30-bit address space. ZONE_DMA32 will cover the rest
> + * of the 32 bit addressable memory area.
>   */
>  phys_addr_t arm64_dma_phys_limit __ro_after_init;
>  static phys_addr_t arm64_dma32_phys_limit __ro_after_init;



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