Re: [PATCH 1/2] dma-mapping: add a dma_ops_bypass flag to struct device

From: Christoph Hellwig
Date: Tue Mar 24 2020 - 03:55:18 EST


On Tue, Mar 24, 2020 at 12:00:09PM +0530, Aneesh Kumar K.V wrote:
> dma_addr_t dma_direct_map_page(struct device *dev, struct page *page,
> unsigned long offset, size_t size, enum dma_data_direction dir,
> unsigned long attrs)
> {
> phys_addr_t phys = page_to_phys(page) + offset;
> dma_addr_t dma_addr = phys_to_dma(dev, phys);
>
> if (unlikely(!dma_capable(dev, dma_addr, size, true))) {
> return iommu_map(dev, phys, size, dir, attrs);
>
> return DMA_MAPPING_ERROR;

If powerpc hardware / firmware people really come up with crap that
stupid you'll have to handle it yourself and will always pay the
indirect call penality.