Re: [PATCH] MIPS: pci-legacy: Override pci_address_to_pio

["Jiaxun Yang" <jiaxun.yang@flygoat.com>]

在2025年1月15日一月 上午7:38，Arnd Bergmann写道：
[...]
>
> Where "range->cpu_addr" is the phys_addr_t location of the
> MMIO window that maps the host controllers port ranges, i.e.
> the fully translated address from the "ranges" property.

This is valid for MIPS's PCI_DRIVERS_GENERIC, but not for PCI_DRIVERS_LEGACY,
which have it's own implementation of various functions. See
arch/mips/pci/pci-legacy.c, pci_load_of_ranges. The address translation
is handled by io_map_base, which usually comes from mips_io_port_base.

>
> The point of the pci_address_to_pio() function is to convert
> this into the Linux-internal virtual port number that gets
> used as an argument to inb()/outb() and reported in
> /proc/ioports and that may or may not be the same as the
> address on the bus itself, depending on the how the translation
> gets set up.
>
> On loongson, we seem to have two port ranges that are set up
> like
>
>                 isa@18000000 {
>                         compatible = "isa";
>                         ranges = <1 0x0 0x0 0x18000000 0x4000>;
>                 };
>
>                 pci@1a000000 {
>                         ranges = <0x01000000 0x0 0x00020000 0x0 
> 0x18020000 0x0 0x00020000>,
>                                  <0x02000000 0x0 0x40000000 0x0 
> 0x40000000 0x0 0x40000000>;
>                 }
>
> Here, the cpu_addr is 0x18000000 for the isa bus and 
> 0x18020000 for the PCI bus, apparently the intention being that
> these are consecutive in physical space, though Linux is free
> to rearrange the logical port numbers in a different way, e.g.
> to ensure that the PCI bus can use port numbers below 0x10000.
>
> On Malta, I see a very strange
>
>         isa {
>                 compatible = "isa";
>                 ranges = <1 0 0 0x1000>;
>         };
>
> which maps the first 4096 port numbers into cpu_addr=0x0. The
> actual port window appears to be at a board specific location
>
> #define MALTA_GT_PORT_BASE      get_gt_port_base(GT_PCI0IOLD_OFS)
> #define MALTA_BONITO_PORT_BASE  ((unsigned long)ioremap (0x1fd00000, 0x10000))
> #define MALTA_MSC_PORT_BASE     get_msc_port_base(MSC01_PCI_SC2PIOBASL)
>
> So e.g. on Bonito, the ranges property would have to be
>
>       ranges = <1 0 0x1fd00000 0x1000>;
>
> Not sure if this is patched in by the bootloader, or where the
> corresponding window for PCI gets defined, but I suspect that
> the reason for the regression is that the caller of
> pci_address_to_pio() accidentally passed in '0' instead of
> the physical address, and it happened to work because of the
> missing PCI_IOBASE definition but broke after that got defined.

Many other pci-legacy drivers are also working this way, PCI core
is not aware of virtual port to physical MMIO address mapping.
PCI core just see it as x86 style port.

Thanks

>
>        Arnd

-- 
- Jiaxun