[U-Boot] [U-Boot, V3, 2/3] ARM: tegra: reserve unmapped RAM so EFI doesn't use it

[Stephen Warren]

On 09/01/2018 03:58 AM, Alexander Graf wrote:
>> From: Stephen Warren <swarren at nvidia.com>
>>
>> Tegra U-Boot ensures that board_get_usable_ram_top() never returns a value
>> over 4GB, since some peripherals can't access such addresses. However, on
>> systems with more than 2GB of RAM, RAM bank 1 does describe this extra
>> RAM, so that Linux (or whatever OS) can use it, subject to DMA
>> limitations. Since board_get_usable_ram_top() points at the top of RAM
>> bank 0, the memory locations describes by RAM bank 1 are not mapped by
>> U-Boot's MMU configuration, and so cannot be used for anything.
>>
>> For some completely inexplicable reason, U-Boot's EFI support ignores the
>> value returned by board_get_usable_ram_top(), and EFI memory allocation
>> routines will return values above U-Boot's RAM top. This causes U-Boot to
>> crash when it accesses that RAM, since it isn't mapped by the MMU. One
>> use-case where this happens is TFTP download of a file on Jetson TX1
>> (p2371-2180).
>>
>> This change explicitly tells the EFI code that this extra RAM should not
>> be used, thus avoiding the crash.
>>
>> A previous attempt to make EFI honor board_get_usable_ram_top() was
>> rejected. So, this patch will need to be replicated for any board that
>> implements board_get_usable_ram_top().
>>
>> Fixes: aa909462d018 ("efi_loader: efi_allocate_pages is too restrictive")
>> Signed-off-by: Stephen Warren <swarren at nvidia.com>
> 
> Thanks, applied to efi-next

They don't seem to have shown up in u-boot/master though...