Re: [RFC PATCH v3 4/6] swiotlb: Add restricted DMA alloc/free support.

[Christoph Hellwig <hch@xxxxxx>]

> +#ifdef CONFIG_SWIOTLB
> +     if (unlikely(dev->dma_io_tlb_mem))
> +             return swiotlb_alloc(dev, size, dma_handle, attrs);
> +#endif

Another place where the dma_io_tlb_mem is useful to avoid the ifdef.

> -phys_addr_t swiotlb_tbl_map_single(struct device *hwdev, phys_addr_t 
> orig_addr,
> -             size_t mapping_size, size_t alloc_size,
> -             enum dma_data_direction dir, unsigned long attrs)
> +static int swiotlb_tbl_find_free_region(struct device *hwdev,
> +                                     dma_addr_t tbl_dma_addr,
> +                                     size_t alloc_size,
> +                                     unsigned long attrs)

> +static void swiotlb_tbl_release_region(struct device *hwdev, int index,
> +                                    size_t size)

This refactoring should be another prep patch.


> +void *swiotlb_alloc(struct device *dev, size_t size, dma_addr_t *dma_handle,
> +                 unsigned long attrs)

I'd rather have the names convey there are for the per-device bounce
buffer in some form.

> +     struct io_tlb_mem *mem = dev->dma_io_tlb_mem;

While we're at it I wonder if the io_tlb is something we could change
while we're at it.  Maybe replace io_tlb_mem with struct swiotlb
and rename the field in struct device to dev_swiotlb?

> +     int index;
> +     void *vaddr;
> +     phys_addr_t tlb_addr;
> +
> +     size = PAGE_ALIGN(size);
> +     index = swiotlb_tbl_find_free_region(dev, mem->start, size, attrs);
> +     if (index < 0)
> +             return NULL;
> +
> +     tlb_addr = mem->start + (index << IO_TLB_SHIFT);
> +     *dma_handle = phys_to_dma_unencrypted(dev, tlb_addr);
> +
> +     if (!dev_is_dma_coherent(dev)) {
> +             unsigned long pfn = PFN_DOWN(tlb_addr);
> +
> +             /* remove any dirty cache lines on the kernel alias */
> +             arch_dma_prep_coherent(pfn_to_page(pfn), size);

Can we hook in somewhat lower level in the dma-direct code so that all
the remapping in dma-direct can be reused instead of duplicated?  That
also becomes important if we want to use non-remapping uncached support,
e.g. on mips or x86, or the direct changing of the attributes that Will
planned to look into for arm64.