On Tue, Sep 12, 2023 at 4:01 PM Hui Fang <hui.fang@xxxxxxx> wrote: > > On Tue, Sep 12 2023 at 11:22 AM Tomasz Figa <tfiga@xxxxxxxxxxxx> > > On Mon, Sep 11, 2023 at 3:13 PM Hui Fang <hui.fang@xxxxxxx> wrote: > > > > > > On Wed, Sep 6, 2023 at 18:28 PM Tomasz Figa <tfiga@xxxxxxxxxxxx> > > wrote: > > > > That all makes sense, but it still doesn't answer the real question > > > > on why swiotlb ends up being used. I think you may want to trace > > > > what happens in the DMA mapping ops implementation on your system > > > > causing it to use swiotlb. > > > > > > Add log and feed invalid data to low buffer on purpose, it's confirmed > > > that swiotlb is actually used. > > > > > > > Yes, that we already know. But why? > > > The physical address of v4l2 buffer is large than 4G (5504139264), so the swiotlb is used. > "[ 846.570271][ T138] software IO TLB: ==== swiotlb_bounce: DMA_TO_DEVICE, > dst 000000004589fa38, src 00000000c6d7e8d8, srcPhy 5504139264, size 4096". Is your DMA device restricted only to the bottom-most 4 GB (32-bit DMA address)? If yes, would it make sense to also allocate from that area rather than bouncing the memory? Best regards, Tomasz
