Hi Lorenzo, I came across this issue when implementing a Linux NVMe endpoint function driver under the Linux PCI Endpoint Framework: https://lwn.net/Articles/804369/ I needed to map up to 128GB of host memory using a single ATU window from the endpoint side because NVMe PRPs can be scattered all over host memory. In the process, I came across this 4GB limitation where the maximum size of memory that can be mapped is limited by what a u32 value can represent. I submitted a separate patch to fix an undefined behavior that may also happen in dw_pcie_prog_outbound_atu_unroll() under some circumstances when the size of the memory being mapped is greater than what a u32 value can represent. https://patchwork.kernel.org/patch/11469701/ The above patch has been accepted. However, the variable pp->mem_size in dw_pcie_host_init() is still a u32 whereas the value returned by resource_size() is u64. If the resource size has non-zero upper 32-bits, those upper 32-bits will be lost when assigning: pp->mem_size = resource_size(pp->mem). Since current callers seem happy with the existing 4GB implementation and fixing the u32 limit is beyond my available resources and has a long high-impact tail, a warning seemed to be a good choice to highlight this issue in case someone else decides to map a MEM region that is greater than 4GB. Removing the warning will avoid such discussions. Without this warning, this limitation will go unnoticed and will only impact whoever has to deal with it. It cost me time to figure it out when I had an application that needed a region larger than 4GB. I figured the most I could do about it is to raise the issue by adding a warning. Regards, Alan
