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Date:   Wed, 3 Jun 2020 20:06:24 +0300
From:   Mike Rapoport <rppt@linux.ibm.com>
To:     Miles Chen <miles.chen@mediatek.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Matthias Brugger <matthias.bgg@gmail.com>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        linux-mediatek@lists.infradead.org, wsd_upstream@mediatek.com
Subject: Re: [PATCH] mm/memblock: export max_pfn for kernel modules
Message-ID: <20200603170624.GA202648@linux.ibm.com>
References: <20200603161132.2441-1-miles.chen@mediatek.com>
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On Thu, Jun 04, 2020 at 12:11:32AM +0800, Miles Chen wrote:
> max_pfn is uesd to get the highest pfn in the system. Drivers like
> drivers/iommu/mtk_iommu.c checks max_pfn to see if it should enable
> its "4GB mode".
> 
> This patch exports the max_pfn symbol, so we can build the driver as
> a kernel module.

You can use totalram_pages(), like e.g.
drivers/media/platform/mtk-vpu/mtk_vpu.c:

$ git grep -np totalram_pages drivers/media/
drivers/media/platform/mtk-vpu/mtk_vpu.c=779=static int mtk_vpu_probe(struct platform_device *pdev)
drivers/media/platform/mtk-vpu/mtk_vpu.c:861:   vpu->enable_4GB = !!(totalram_pages() > (SZ_2G >> PAGE_SHIFT));


> Signed-off-by: Miles Chen <miles.chen@mediatek.com>
> ---
>  mm/memblock.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/mm/memblock.c b/mm/memblock.c
> index c79ba6f9920c..3b2b21ecebb6 100644
> --- a/mm/memblock.c
> +++ b/mm/memblock.c
> @@ -99,6 +99,7 @@ EXPORT_SYMBOL(contig_page_data);
>  unsigned long max_low_pfn;
>  unsigned long min_low_pfn;
>  unsigned long max_pfn;
> +EXPORT_SYMBOL(max_pfn);
>  unsigned long long max_possible_pfn;
>  
>  static struct memblock_region memblock_memory_init_regions[INIT_MEMBLOCK_REGIONS] __initdata_memblock;
> -- 
> 2.18.0

-- 
Sincerely yours,
Mike.