linux-kernel - Re: [PATCH v3 8/8] mm: Update DMA zones description

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Message-ID: <20201015054026.GC12218@lst.de>
Date:   Thu, 15 Oct 2020 07:40:26 +0200
From:   Christoph Hellwig <hch@....de>
To:     Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
Cc:     robh+dt@...nel.org, catalin.marinas@....com, hch@....de,
        ardb@...nel.org, linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        robin.murphy@....com, linux-arm-kernel@...ts.infradead.org,
        linux-rpi-kernel@...ts.infradead.org, jeremy.linton@....com,
        iommu@...ts.linux-foundation.org, devicetree@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [PATCH v3 8/8] mm: Update DMA zones description

On Wed, Oct 14, 2020 at 09:12:10PM +0200, Nicolas Saenz Julienne wrote:
> The default behavior for arm64 changed, so reflect that.
> 
> Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
> Acked-by: Catalin Marinas <catalin.marinas@....com>
> ---
>  include/linux/mmzone.h | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index fb3bf696c05e..4ee2306351b9 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -363,8 +363,9 @@ enum zone_type {
>  	 *  - arm only uses ZONE_DMA, the size, up to 4G, may vary depending on
>  	 *    the specific device.
>  	 *
> -	 *  - arm64 has a fixed 1G ZONE_DMA and ZONE_DMA32 for the rest of the
> -	 *    lower 4G.
> +	 *  - arm64 uses a single 4GB ZONE_DMA, except on the Raspberry Pi 4,
> +	 *    in which ZONE_DMA covers the first GB and ZONE_DMA32 the rest of
> +	 *    the lower 4GB.

Honestly I think this comment just needs to go away.  We can't really list
every setup in a comment in common code.