Re: [U-Boot] [PATCH] ARM: make ARMV7_LPAE select PHYS_64BIT

[Masahiro Yamada]

Hi Alex,


2016-08-11 22:50 GMT+09:00 Alexander Graf :
>
>
> On 11.08.16 15:36, Masahiro Yamada wrote:
>> As you see in arch/arm/include/asm/types.h, CONFIG_PHYS_64BIT
>> determines the size of phys_addr_t.  The ARM Large Physical Address
>> Extension allows CPUs to access a physical address space larger than
>> 4GB, so the physical address may not fit in 32bit long phys_addr_t.
>>
>> Signed-off-by: Masahiro Yamada 
>> ---
>>
>> I did Buildman test, but not run-time test.
>>
>> Looks like bcm283x (RPI) is the only arch that selects ARMV7_LPAE,
>> so I hope Stephen will check this patch.
>
> Well, the bcm2837 still only has a 32bit bus, so we can't actually make
> use of addresses bigger than 32bits.
>
> I think it would make most sense to select PHYS_64BIT on whatever 32bit
> SoC actually needs to accesses memory above 4GB.
>
> The main reason for having LPAE support for armv7 is not to support
> higher addresses (we still map everything 1:1 usually), it's to allow
> running in HYP mode which requires LPAE style page tables.

Thanks for explaining this.
Then, please forget about this patch.


-- 
Best Regards
Masahiro Yamada
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Re: [U-Boot] [PATCH] ARM: make ARMV7_LPAE select PHYS_64BIT

[Stephen Warren]

On 08/11/2016 07:36 AM, Masahiro Yamada wrote:

As you see in arch/arm/include/asm/types.h, CONFIG_PHYS_64BIT
determines the size of phys_addr_t.  The ARM Large Physical Address
Extension allows CPUs to access a physical address space larger than
4GB, so the physical address may not fit in 32bit long phys_addr_t.

Signed-off-by: Masahiro Yamada 
---

I did Buildman test, but not run-time test.

Looks like bcm283x (RPI) is the only arch that selects ARMV7_LPAE,
so I hope Stephen will check this patch.


Tested-by: Stephen Warren 

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Re: [U-Boot] [PATCH] ARM: make ARMV7_LPAE select PHYS_64BIT

[Alexander Graf]

On 11.08.16 15:36, Masahiro Yamada wrote:
> As you see in arch/arm/include/asm/types.h, CONFIG_PHYS_64BIT
> determines the size of phys_addr_t.  The ARM Large Physical Address
> Extension allows CPUs to access a physical address space larger than
> 4GB, so the physical address may not fit in 32bit long phys_addr_t.
> 
> Signed-off-by: Masahiro Yamada 
> ---
> 
> I did Buildman test, but not run-time test.
> 
> Looks like bcm283x (RPI) is the only arch that selects ARMV7_LPAE,
> so I hope Stephen will check this patch.

Well, the bcm2837 still only has a 32bit bus, so we can't actually make
use of addresses bigger than 32bits.

I think it would make most sense to select PHYS_64BIT on whatever 32bit
SoC actually needs to accesses memory above 4GB.

The main reason for having LPAE support for armv7 is not to support
higher addresses (we still map everything 1:1 usually), it's to allow
running in HYP mode which requires LPAE style page tables.


Alex
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