On Thu, Sep 14, 2023 at 15:41 PM Fang Hui <hui.fang@xxxxxxx> wrote: > On system with "CONFIG_ZONE_DMA32=y", if the allocated physical address is > greater than 4G, swiotlb will be used. It will lead below defects. > 1) Impact performance due to an extra memcpy. > 2) May meet below error due to swiotlb_max_mapping_size() > is 256K (IO_TLB_SIZE * IO_TLB_SEGSIZE). > "swiotlb buffer is full (sz: 393216 bytes), total 65536 (slots), used 2358 (slots)" > > To avoid those defects, use dma_alloc_pages() instead of alloc_pages() in > vb2_dma_sg_alloc_compacted(). > > Suggested-by: Tomasz Figa <tfiga@xxxxxxxxxxxx> > Signed-off-by: Fang Hui <hui.fang@xxxxxxx> --- Two things. 1. For dma_data_direction para (DMA_BIDIRECTIONAL is used) of dma_alloc_pages(), maybe better pass from callers? In DeviceAsWebcam case, it's DMA_TO_DEVICE. 2. "MA-21654" (NXP ticket number) should be removed in the comment, need I re-push or it will be done on your side, thanks! BRs, Fang Hui
