PCI endpoint: pci-epf-test is broken on big-endian

[Niklas Cassel <cassel@kernel.org>]

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.

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