Avalon-MM PCIe DMA Controller busy forever with some hosts
I've been using Cyclone V device that communicates with a host PC via
PCI Express. The communication logic is built using Qsys "Avalon-MM Cyclone V Hard IP for PCI Express". On the host PC (x86-64), CentOS 6.x (Linux kernel 2.6.x) is running. The system has been working fine for more than a year without problem. Recently, however, I noticed that the DMA write (memory write initiated by the device) does not work properly on CentOS 7.x (kernel 3.10.x). Note that other functions including PCI configuration read/write and the host initiated memory read/write are working fine. DMA read is not implemented and thus not tested. Looking inside the status register of Qsys DMA Controller, I found that the bit1 remains high forever, which means DMA is started but never completes. I am sure the following registers are properly set before starting the DMA. The value of address 03h (length register) does not decrement at all, even a few minutes after the kicking off of the DMA. 01h readaddress RW start address of a read. 02h writeaddress RW start address of a write. 03h length RW length in bytes. decrements to 0 as the transfer proceeds. 06h control RW So my question is: what can make the DMA controller busy forever? If a wrong value is set to 02h (writeaddress), could that cause the DMA controller behave like this? Please help. Any idea or suggestion would be greatly appreciated.