On Tuesday 27 September 2011, Mark Salter wrote:
> +dma_addr_t dma_map_single(struct device *dev, void *ptr, size_t size,
> + enum dma_data_direction dir)
> +{
> + dma_addr_t addr = virt_to_phys(ptr);
> +
> + BUG_ON(!valid_dma_direction(dir));
> +
> + switch (dir) {
> + case DMA_FROM_DEVICE:
> + L2_cache_block_invalidate(addr, addr + size);
> + break;
> + case DMA_TO_DEVICE:
> + L2_cache_block_writeback(addr, addr + size);
> + break;
> + case DMA_BIDIRECTIONAL:
> + /*
> + * If area will be used bidirectionally, syncing will
> + * take place manually in the driver.
> + */
I think this comment is not strictly correct and you have to do a
writeback+invalidate here. When you map an area, it initially
belongs to the device, until you either do an unmap or sync_*_for_cpu.
> +void dma_unmap_single(struct device *dev, dma_addr_t handle,
> + size_t size, enum dma_data_direction dir)
> +{
> + /* nothing to do here */
> + debug_dma_unmap_page(dev, handle, size, dir, true);
> +}
> +EXPORT_SYMBOL(dma_unmap_single);
> +void dma_sync_single_for_cpu(struct device *dev, dma_addr_t handle,
> + size_t size, enum dma_data_direction dir)
> +{
> + unsigned long paddr = handle;
> +
> + BUG_ON(!valid_dma_direction(dir));
> +
> + switch (dir) {
> + case DMA_FROM_DEVICE:
> + L2_cache_block_invalidate(paddr, paddr + size);
> + break;
> + case DMA_TO_DEVICE:
> + L2_cache_block_writeback(paddr, paddr + size);
> + break;
> + case DMA_BIDIRECTIONAL:
> + L2_cache_block_writeback_invalidate(paddr, paddr + size);
> + break;
> + default:
> + break;
> + }
> +
> + debug_dma_sync_single_for_cpu(dev, handle, size, dir);
> +}
> +EXPORT_SYMBOL(dma_sync_single_for_cpu);
Normally, sync_*_for_cpu is the same as unmap regarding the cache.
> +void dma_sync_single_for_device(struct device *dev, dma_addr_t handle,
> + size_t size, enum dma_data_direction dir)
> +{
> + unsigned long paddr = handle;
> +
> + BUG_ON(!valid_dma_direction(dir));
> +
> + /* don't bother invalidating if DMA to device */
> + if (dir != DMA_TO_DEVICE)
> + L2_cache_block_invalidate(paddr, paddr + size);
> +
> + debug_dma_sync_single_for_device(dev, handle, size, dir);
> +}
> +EXPORT_SYMBOL(dma_sync_single_for_device);
And this should do the same as map(). In particular it needs
to writeback the cache when direction is TO_DEVICE or BIDIRECTIONAL.
Arnd
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