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Date: Fri, 1 Feb 2013 13:40:29 +0800
From: Hui Wang <jason77.wang@gmail.com>
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To: Nicolas Pitre <nicolas.pitre@linaro.org>
CC: Hui Wang <jason77.wang@gmail.com>, Cyril Chemparathy <cyril@ti.com>,
        Russell King - ARM Linux <linux@arm.linux.org.uk>,
        <linux-arm-kernel@lists.infradead.org>, <linux-kernel@vger.kernel.org>,
        <marc.zyngier@arm.com>, <sboyd@codeaurora.org>,
        <linus.walleij@linaro.org>, Will Deacon <will.deacon@arm.com>,
        Vitaly Andrianov <vitalya@ti.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        <paulmck@linux.vnet.ibm.com>
Subject: Re: [PATCH v4 02/13] ARM: LPAE: use phys_addr_t in alloc_init_pud()
References: <1359669512-31276-1-git-send-email-cyril@ti.com> <1359669512-31276-3-git-send-email-cyril@ti.com> <510B327E.3050502@gmail.com> <alpine.LFD.2.02.1301312218270.6300@xanadu.home>
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Nicolas Pitre wrote:
> On Fri, 1 Feb 2013, Hui Wang wrote:
>
>   
>> Cyril Chemparathy wrote:
>>     
>>> From: Vitaly Andrianov <vitalya@ti.com>
>>>
>>> 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@ti.com>
>>> Signed-off-by: Cyril Chemparathy <cyril@ti.com>
>>> Acked-by: Nicolas Pitre <nico@linaro.org>
>>> Acked-by: Catalin Marinas <catalin.marinas@arm.com>
>>> ---
>>>  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
>
>