Re: [PATCH v2] dma-mapping: fix dma_addressing_limited if dma_range_map can't cover all system RAM

[Robin Murphy]

On 2023-10-10 08:48, Christoph Hellwig wrote:
> dma_addressing_limited is called for every dma (direct) map, and this
> new code is way to heavy for that.  We'll need to cache the information
> somehow.

But is it? That was my instinctive reaction as well, but AFAICS it is 
only actually used by drivers in setup paths, either directly or via 
dma_max_mapping_size(). The dma_capable() check which we *do* use for 
every actual mapping still just checks whether the given physical 
address exists in the range map. I believe the underlying problem here 
is when dma_capable() say the mapping needs bouncing, but then it's too 
big for that to succeed, since dma_max_mapping_size() gave the wrong 
answer to start with.

Thanks,
Robin.