ARM_LPAE + VMSPLIT_2G cause swiotlb warning on Raspberry Pi 4

[Arnd Bergmann]

On Wed, May 17, 2023, at 12:34, Arnd Bergmann wrote:
> 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:
>
> 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.

It looks like Arm does not set the ARCH_LOW_ADDRESS_LIMIT
constant for swiotlb, so it gets the default 4GB maximum.

I think this would work on arm, though it's probably not the
correct fix in general, as I think MAX_DMA_ADDRESS is meant
to refer to the ISA_DMA_API limit, not the ZONE_DMA limit.:

--- a/include/linux/memblock.h
+++ b/include/linux/memblock.h
@@ -394,7 +394,7 @@ static inline int memblock_get_region_node(const struct memblock_region *r)
 #define MEMBLOCK_LOW_LIMIT 0
 
 #ifndef ARCH_LOW_ADDRESS_LIMIT
-#define ARCH_LOW_ADDRESS_LIMIT  0xffffffffUL
+#define ARCH_LOW_ADDRESS_LIMIT  MAX_DMA_ADDRESS
 #endif
 
 phys_addr_t memblock_phys_alloc_range(phys_addr_t size, phys_addr_t align,

Can you give this a try?

      Arnd