ARM_LPAE + VMSPLIT_2G cause swiotlb warning on Raspberry Pi 4

[Arnd Bergmann]

On Wed, May 17, 2023, at 12:24, Stefan Wahren wrote:
> Am 17.05.23 um 12:06 schrieb Robin Murphy:
>> On 2023-05-17 07:23, Stefan Wahren wrote:
>>> Am 17.05.23 um 00:17 schrieb Florian Fainelli:
>> This suggests that the SWIOTLB buffer itself has somehow been allocated 
>> from ZONE_NORMAL rather than ZONE_DMA (unfortunately you trimmed the log 
>> line from swiotlb_print_info() saying exactly where it is). That can't 
>> happen with VMSPLIT_3G where we have less than 1GB of lowmem anyway, 
>> which explains that difference. I don't have an idea off-hand why LPAE 
>> would affect it.

I think LPAE doesn't affect it, the configurations that Stefan
mentioned were LPAE with VMSPLIT_2G (broken), non-LPAE with
VMSPLIT_3G (works) and LPAE with VMSPLIT_3G (works). I would assume
that non-LPAE with VMSPLIT_2G or VMSPLIT_3G_OPT is also broken.

> This one?
> [    0.000000] software IO TLB: area num 4.
> [    0.000000] software IO TLB: mapped [mem 
> 0x0000000069e7f000-0x000000006de7f000] (64MB)

Indeed, that is clearly above the .dma_zone_size value from
the machine descriptor.

     Arnd