On 10/21/24 16:49, Niklas Cassel wrote: > Hello PCI endpoint maintainers, > > > While looking at the pci-epf-test.c driver, I noticed that > pci-epf-test is completely broken with regards to endianness. > > As you probably know, PCI devices are inherently little-endian, > and the data stored in the PCI BARs should be in little-endian. > > However, pci-epf-test does no conversion before storing the data > to backing memory, and no conversion after reading the data from > backing memory. > > For the data backing test_reg BAR (usually BAR0), which has the > format as defined by struct pci_epf_test_reg, is simply stored > to memory using e.g.: > reg->status = STATUS_WRITE_SUCCESS; > > Surely, this should be: > reg->status = cpu_to_le32(STATUS_WRITE_SUCCESS); > > > Likewise the src and dst address is accessed simply by > reg->dst_addr and reg->src_addr. > > Surely, this should be accessed using: > dst_addr = le64_to_cpu(reg->dst_addr); > src_addr = le64_to_cpu(reg->src_addr); > > So bottom line, pci-epf-test will currently not behave correctly > on big-endian. > > > > Looking at pci-endpoint-test however, it does all its accesses using > readl() and writel(), and if you look at the implementations of > readl()/writel(): > https://github.com/torvalds/linux/blob/v6.12-rc4/include/asm-generic/io.h#L181-L184 > > They convert to CPU native after reading, and convert to little-endian > before writing, so pci-endpoint-test (RC side driver) is okay, it is > just pci-epf-test (EP side driver) that is broken. That in itself is another problem. The use of readl/writel for things in the EPF BAR memory is also *wrong*, because that memory is NOT a real mmio memory. We should be using READ_ONCE()/WRITE_ONCE() to treat the BAR as volatile memory but not use readl/writel. > > I'm not planning on spending time on this, but I thought that I ought to at > least report it, such that maintainers/developers/users are aware of it. > > > Kind regards, > Niklas -- Damien Le Moal Western Digital Research
