Messages in this thread | | | Date | Fri, 1 Feb 2013 12:56:54 -0500 | From | Cyril Chemparathy <> | Subject | Re: [PATCH v4 02/13] ARM: LPAE: use phys_addr_t in alloc_init_pud() |
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On 02/01/2013 12:33 PM, Subash Patel wrote: > 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@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. > > 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. >
On the KeyStone platform, memory is located at 08:0000:0000, i.e., outside the 32-bit addressable range. The hardware provides a limited aliased map of the very same memory at 8000:0000, but this alias is limited and intended only for boot time usage.
We boot the system while running out of this 32-bit physical address range. We then switch over to the high physical address range fairly early in the kernel boot, by rewriting boot-time page tables and the TTBRs. Once this switch over has happened, lowmem is indeed outside the 32-bit physical address space.
Thanks -- Cyril.
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