[PATCH 4/6] imx8m: Restrict usable memory to space below 4G boundary

[Peng Fan (OSS)]

On 2021/6/7 20:38, Marek Vasut wrote:
> On 6/7/21 2:05 PM, Frieder Schrempf wrote:
>> From: Frieder Schrempf <frieder.schrempf at kontron.de>
>>
>> Some IPs have their accessible address space restricted by the
>> interconnect. Let's make sure U-Boot only ever uses the space below
>> the 4G address boundary (which is 3GiB big), even when the effective
>> available memory is bigger.
>>
>> We implement board_get_usable_ram_top() for all i.MX8M SoCs, as the
>> whole family is affected by this.
> 
> Shouldn't only those specific IP drivers handle buffers in the 64bit 
> space somehow ? E.g. using a bounce buffer ?

That could cause extra mem copy. Bounce buffer would be good for systems
that take U-Boot as UEFI firmware, because U-Boot would be located at
high end, but in the middle just top of 4GB.

I not object this patch, but it also be good if bounce buffer be added
for improvement.

Reviewed-by: Peng Fan <peng.fan at nxp.com>