On Mon, May 10, 2021 at 11:05 PM Christoph Hellwig hch@lst.de wrote:

...

+static inline bool is_dev_swiotlb_force(struct device *dev) +{ +#ifdef CONFIG_DMA_RESTRICTED_POOL

• if (dev->dma_io_tlb_mem)
  

•         return true;
  

+#endif /* CONFIG_DMA_RESTRICTED_POOL */

• return false;
  

+}

...

  /* If SWIOTLB is active, use its maximum mapping size */
  if (is_swiotlb_active(dev) &&

•     (dma_addressing_limited(dev) || swiotlb_force == SWIOTLB_FORCE))
  

•     (dma_addressing_limited(dev) || swiotlb_force == SWIOTLB_FORCE ||
  

•      is_dev_swiotlb_force(dev)))
  

This is a mess. I think the right way is to have an always_bounce flag in the io_tlb_mem structure instead. Then the global swiotlb_force can go away and be replace with this and the fact that having no io_tlb_mem structure at all means forced no buffering (after a little refactoring).

Will do in the next version.