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It would have been easier >> to debug the issue if dma_addressing_limited() had a warning about a >> device not being able to address all of memory and thus forcing all >> accesses through a bounce buffer. Please see[2]. >> >> A warning would have let the user of the system know that in their >> particular case, use_dma32 is set due to the addressing limitation >> and this would impact performance of the driver in use. >> >> Implement a WARN_ONCE() to point to the potential use of bounce buffers >> when we hit the condition. When swiotlb is used, >> dma_addressing_limited() is used to determine the size of maximum dma >> buffer size in dma_direct_max_mapping_size(). The warning could be >> triggered in that check as well. > > dma_addressing_limited is a perfectly expected condition, and returns > true for many devices and still plenty system configuation. A kernel > warning with a stacktrace is not acceptable for that. A simple one-line > dev_info might be ok, but could still be rather spammy on many systems. > Thanks for the review! I'll convert it to a dev_info(). We can remove it, if it causes confusion or users complain about it? Balbir