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Subject: Re: [PATCH] arm64: mm: make CONFIG_ZONE_DMA32 configurable
To:     Miles Chen <miles.chen@mediatek.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will.deacon@arm.com>
Cc:     linux-mediatek@lists.infradead.org, linux-kernel@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, wsd_upstream@mediatek.com
References: <1558973315-19655-1-git-send-email-miles.chen@mediatek.com>
From:   Robin Murphy <robin.murphy@arm.com>
Message-ID: <814b9bd0-38de-4b8d-92b3-d663931d90bf@arm.com>
Date:   Tue, 28 May 2019 11:43:11 +0100
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On 27/05/2019 17:08, Miles Chen wrote:
> This change makes CONFIG_ZONE_DMA32 defuly y and allows users
> to overwrite it.
> 
> For the SoCs that do not need CONFIG_ZONE_DMA32, this is the
> first step to manage all available memory by a single
> zone(normal zone) to reduce the overhead of multiple zones.
> 
> The change also fixes a build error when CONFIG_NUMA=y and
> CONFIG_ZONE_DMA32=n.
> 
> arch/arm64/mm/init.c:195:17: error: use of undeclared identifier 'ZONE_DMA32'
>                  max_zone_pfns[ZONE_DMA32] = PFN_DOWN(max_zone_dma_phys());
> 
> Signed-off-by: Miles Chen <miles.chen@mediatek.com>
> ---
>   arch/arm64/Kconfig   | 3 ++-
>   arch/arm64/mm/init.c | 2 ++
>   2 files changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 76f6e4765f49..9d20a736d1d1 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -260,7 +260,8 @@ config GENERIC_CALIBRATE_DELAY
>   	def_bool y
>   
>   config ZONE_DMA32
> -	def_bool y
> +	bool "Support DMA32 zone"

This probably warrants an "if EMBEDDED" or "if EXPERT", since turning it 
off produces a kernel which won't work at all on certain systems (I've 
played around with this before...)

> +	default y
>   
>   config HAVE_GENERIC_GUP
>   	def_bool y
> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> index d2adffb81b5d..96829ce21f99 100644
> --- a/arch/arm64/mm/init.c
> +++ b/arch/arm64/mm/init.c
> @@ -191,8 +191,10 @@ static void __init zone_sizes_init(unsigned long min, unsigned long max)
>   {
>   	unsigned long max_zone_pfns[MAX_NR_ZONES]  = {0};
>   
> +#ifdef CONFIG_ZONE_DMA32
>   	if (IS_ENABLED(CONFIG_ZONE_DMA32))

There's no point keeping the IS_ENABLED() check when it's entirely 
redundant with the #ifdefs.

Robin.

>   		max_zone_pfns[ZONE_DMA32] = PFN_DOWN(max_zone_dma_phys());
> +#endif
>   	max_zone_pfns[ZONE_NORMAL] = max;
>   
>   	free_area_init_nodes(max_zone_pfns);
>