Messages in this thread | | | Date | Fri, 01 Feb 2013 09:33:56 -0800 | From | Subash Patel <> | Subject | Re: [PATCH v4 02/13] ARM: LPAE: use phys_addr_t in alloc_init_pud() |
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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.
Regards, Subash
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