linux-kernel - Re: [PATCH] mm/memblock: export max

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Message-ID: <1591241986.29475.18.camel@mtkswgap22>
Date:   Thu, 4 Jun 2020 11:39:46 +0800
From:   Miles Chen <miles.chen@...iatek.com>
To:     Mike Rapoport <rppt@...ux.ibm.com>
CC:     Andrew Morton <akpm@...ux-foundation.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-mediatek@...ts.infradead.org>, <wsd_upstream@...iatek.com>
Subject: Re: [PATCH] mm/memblock: export max_pfn for kernel modules

On Wed, 2020-06-03 at 20:06 +0300, Mike Rapoport wrote:
> 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/medhttps://lkml.org/lkml/2020/5/30/123ia/
> 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));
> 

Thanks for the suggestion.
totalram_pages() works and I can follow this example.

Miles

> 
> > Signed-off-by: Miles Chen <miles.chen@...iatek.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
>