Re: [PATCH v4 02/13] ARM: LPAE: use phys_addr_t in alloc_init_pud()

[Hui Wang]

Nicolas Pitre wrote:
> On Fri, 1 Feb 2013, Hui Wang wrote:
>
>   
> > Cyril Chemparathy wrote:
> >     
> > > From: Vitaly Andrianov <vitalya@xxxxxx>
> > >
> > > This patch fixes the alloc_init_pud() function to use phys_addr_t instead of
> > > unsigned long when passing in the phys argument.
> > >
> > > This is an extension to commit 97092e0c56830457af0639f6bd904537a150ea4a
> > > (ARM:
> > > pgtable: use phys_addr_t for physical addresses), which applied similar
> > > changes
> > > elsewhere in the ARM memory management code.
> > >
> > > Signed-off-by: Vitaly Andrianov <vitalya@xxxxxx>
> > > Signed-off-by: Cyril Chemparathy <cyril@xxxxxx>
> > > Acked-by: Nicolas Pitre <nico@xxxxxxxxxx>
> > > Acked-by: Catalin Marinas <catalin.marinas@xxxxxxx>
> > > ---
> > >  arch/arm/mm/mmu.c |    3 ++-
> > >  1 file changed, 2 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/arch/arm/mm/mmu.c b/arch/arm/mm/mmu.c
> > > index 9f06102..ef43689 100644
> > > --- a/arch/arm/mm/mmu.c
> > > +++ b/arch/arm/mm/mmu.c
> > > @@ -612,7 +612,8 @@ static void __init alloc_init_section(pud_t *pud,
> > > unsigned long addr,
> > >  }
> > >   static void __init alloc_init_pud(pgd_t *pgd, unsigned long addr,
> > > -	unsigned long end, unsigned long phys, const struct mem_type *type)
> > > +				  unsigned long end, phys_addr_t phys,
> > > +				  const struct mem_type *type)
> > >   
> > >       
> > The change is correct but seems useless so far. This function only be called
> > from map_lowmem and devicemaps_init, from i know neither lowmem nor device io
> > registers of existing platforms exceed 32bit address.
> >     
>
> It is not because you are not aware of any existing platforms with RAM 
> or device IO above the 4GB mark that they don't exist.
>
> For example, some LPAE systems have all their RAM located above the 4G 
> physical address mark. A simple (potentially non DMA capable) alias 
> exists in the low 32-bit address space to allow the system to boot and 
> switch to the real physical RAM addresses once the MMU is turned on.  
> Some of that RAM is still qualified as "low mem" i.e. the portion of RAM 
> that the kernel keeps permanently mapped in the 32-bit virtual space 
> even if all of it is above the 4G mark in physical space.
>
>
>   
Got it, thanks for sharing the knowledge.

Regards,
Hui.
> Nicolas
>
>   

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