Hi Arnd,
On 11/21/23 11:03, Arnd Bergmann wrote:
On Mon, Nov 20, 2023, at 22:59, Philipp Stanner wrote:
lib/iomap.c contains one of the definitions of pci_iounmap(). The
current comment above this out-of-place function does not clarify WHY
the function is defined here.
Linus's detailed comment above pci_iounmap() in drivers/pci/iomap.c
clarifies that in a far better way.
Extend the existing comment with an excerpt from Linus's and hint at the
other implementation in drivers/pci/iomap.c
Signed-off-by: Philipp Stanner <pstanner@xxxxxxxxxx>
I think instead of explaining why the code is so complicated
here, I'd prefer to make it more logical and not have to
explain it.
We should be able to define a generic version like
void pci_iounmap(struct pci_dev *dev, void __iomem * addr)
Let's shed some light on the different config options related to this.
To me it looks like GENERIC_IOMAP always implies GENERIC_PCI_IOMAP.
lib/iomap.c contains a definition of pci_iounmap() since it uses the
common IO_COND() macro. This definitions wins if GENERIC_IOMAP was
selected.
lib/pci_iomap.c contains another definition of pci_iounmap() which is
guarded by ARCH_WANTS_GENERIC_PCI_IOUNMAP to prevent multiple definitions
in case either GENERIC_IOMAP is set or the architecture already defined
pci_iounmap().
What's the purpose of not having set ARCH_HAS_GENERIC_IOPORT_MAP producing
an empty definition of pci_iounmap() though [1]?
And more generally, is there any other (subtle) logic behind this?
[1] https://elixir.bootlin.com/linux/latest/source/lib/pci_iomap.c#L167
{
#ifdef CONFIG_HAS_IOPORT
if (iomem_is_ioport(addr)) {
ioport_unmap(addr);
return;
}
#endif
iounmap(addr)
}
and then define iomem_is_ioport() in lib/iomap.c for x86,
while defining it in asm-generic/io.h for the rest,
with an override in asm/io.h for those architectures
that need a custom inb().
So, that would be similar to IO_COND(), right? What would we need inb() for
in this context?
- Danilo
Note that with ia64 gone, GENERIC_IOMAP is not at all
generic any more and could just move it to x86 or name
it something else. This is what currently uses it:
arch/hexagon/Kconfig: select GENERIC_IOMAP
arch/um/Kconfig: select GENERIC_IOMAP
These have no port I/O at all, so it doesn't do anything.
arch/m68k/Kconfig: select GENERIC_IOMAP
on m68knommu, the default implementation from asm-generic/io.h
as the same effect as GENERIC_IOMAP but is more efficient.
On classic m68k, GENERIC_IOMAP does not do what it is
meant to because I/O ports on ISA devices have port
numbers above PIO_OFFSET. Also they don't have PCI.
arch/mips/Kconfig: select GENERIC_IOMAP
This looks completely bogus because it sets PIO_RESERVED
to 0 and always uses the mmio part of lib/iomap.c.
arch/powerpc/platforms/Kconfig: select GENERIC_IOMAP
This is only used for two platforms: cell and powernv,
though on Cell it no longer does anything after the
commit f4981a00636 ("powerpc: Remove the celleb support");
I think the entire io_workarounds code now be folded
back into spider_pci.c if we wanted to.
The PowerNV LPC support does seem to still rely on it.
This tries to do the exact same thing as lib/logic_pio.c
for Huawei arm64 servers. I suspect that neither of them
does it entirely correctly since the powerpc side appears
to just override any non-LPC PIO support while the arm64
side is missing the ioread/iowrite support.
Arnd
