[U-Boot] [PATCH v2 2/6] sunxi: add Kconfig option for the maximum accessible DRAM

Icenowy Zheng
2018-03-23T09:45:45Z

于 2018年3月23日 GMT+08:00 下午5:39:25, Maxime Ripard <maxime.ripard@bootlin.com> 写到:
>On Fri, Mar 23, 2018 at 04:18:53PM +0800, 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.
>
>How would that work in Linux?

From CPU's view only 3GiB DRAM is attached, so Linux can
use the 3GiB space only.

Only the DRAM controller knows that 4GiB DRAM is connected :-)

>
>> Add a Kconfig option for the maximum accessible DRAM.
>>
>> 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.
>
>I guess we have LPAE on armv7 to deal with this nicely.
>
>Maxime