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

[Subash Patel]

Hi Nicolas,

On Thursday 31 January 2013 07:35 PM, 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.

I think he is right. You cannot have low_mem and devices in 36-bit 
areas. Atleast this is what I saw in one of the platforms on which I 
tested these patches. I am not sure what you mean by hardware address 
aliasing(as I have real RAM), but we need 32-bit areas to boot the CPU 
and I have mapped them for the LOW_MEM. But, I have used 36-bit areas 
for the HIGH_MEM. Since you said about aliasing DDR area in 32-bits, and 
then switching to 36-bit RAM, does the dma of the devices still use 
32-bit aliased addresses?

I haven't tested a configuration where LOW_MEM can have both 32-bit and 
36-bit DDR PA though. I think its not possible too.

Regards,
Subash


> Nicolas
> --
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@xxxxxxxxxxxxxxx
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at  http://www.tux.org/lkml/
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/