[U-Boot] [linux-sunxi] Re: [PATCH 2/5] sunxi: add Kconfig option for the maximum accessible DRAM

[Chen-Yu Tsai]

On Thu, Feb 8, 2018 at 8:35 AM, André Przywara <andre.przywara at arm.com> wrote:
> On 07/02/18 19:35, Icenowy Zheng wrote:
>> Allwinner 64-bit SoCs can use 4GiB DRAM chip, however their memory map
>> has only allocated 3GiB for DRAM, so only 3GiB of the DRAM is
>> accessible.
>>
>> Add a Kconfig option for the maximum accessible DRAM.
>
> That looks fine to me, but have you checked CONFIG_MAX_MEM_MAPPED?
> get_effective_memsize() in common/memsize.c looks like it's solving this
> very problem.
>
>> For A80 it should be a much higher value (8GiB), but as I have no A80
>> device to test and originally U-Boot only supports 2GiB DRAM on A80, it
>> currently still falls under the 2GiB situation.
>
> Well, that depends on how we will use SUNXI_DRAM_SIZE. If that's to
> limit the size we eventually report in the DT, that should be indeed 8GB
> on the A80. But U-Boot itself can't use more than 3GB on sunxi/ARMv7
> (due to the static 1:1 mapping).
> I think we should separate those two numbers (actual DRAM size and
> U-Boot's own DRAM size), if we really want to support >3GB on the A80.
>
> But maybe we should not get carried away by something that doesn't
> really exist.

That was the first thing that popped up in my mind after seeing this
series. A80 supports LPAE. However, the A80 is out of production, and
no one produced any boards with more than 2GB of RAM. So >3GB on
sunxi is going to go untested for a long time, if not forever.

ChenYu

>
> Thanks,
> Andre.
>
>>
>> Signed-off-by: Icenowy Zheng <icenowy at aosc.io>
>> ---
>>  arch/arm/mach-sunxi/Kconfig | 7 +++++++
>>  1 file changed, 7 insertions(+)
>>
>> diff --git a/arch/arm/mach-sunxi/Kconfig b/arch/arm/mach-sunxi/Kconfig
>> index 1fededd0a3..32739e0f33 100644
>> --- a/arch/arm/mach-sunxi/Kconfig
>> +++ b/arch/arm/mach-sunxi/Kconfig
>> @@ -63,6 +63,13 @@ config MACH_SUNXI_H3_H5
>>       select SUNXI_GEN_SUN6I
>>       select SUPPORT_SPL
>>
>> +# TODO: try out A80's 8GiB DRAM space
>> +config SUNXI_DRAM_MAX_SIZE
>> +     hex
>> +     default 0xC0000000 if MACH_SUN50I
>> +     default 0xC0000000 if MACH_SUN50I_H5
>> +     default 0x80000000
>> +
>>  choice
>>       prompt "Sunxi SoC Variant"
>>       optional
>>
>
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