Hi, I have a PCIe - SATA bridge device, and I would like to access the I2C control registers in the PCI memory region (BAR5) - these use just two addresses in the BAR. I have tried, in userspace, to mmap() the /sys/bus/pci/devices/..../resource5 file and read from that, but all I get is 0xFF in every byte. I used pcimem (https://github.com/billfarrow/pcimem.git) to try to read the BAR. The device is already matched by the 'ahci' driver, and the attached disks are visible and mountable. If I unbind the ahci driver to use uio, I can of course no longer use the device as a SATA bridge. In other PCI devices which are also matched by ahci, I can mmap and read published BARs fine without unbinding the ahci driver. What is the correct way to fiddle with the memory in the BARs of a PCI device, while still letting the normal driver run the device? I am not doing anything related to AHCI or SATA, just reading and writing to the "side-channel" communication hardware. Best regards, John