Re: [PATCH v2 2/3] PCI: fix 'pci_remap_iospace' for architectures with PCI_IOBASE not defined

[Bjorn Helgaas <helgaas@kernel.org>]

[+cc Liviu, Rob, Catalin, Arnd, since this warning was added by
8b921acfeffd ("PCI: Add pci_remap_iospace() to map bus I/O resources"),
https://git.kernel.org/linus/8b921acfeffd]

On Sun, Aug 22, 2021 at 06:10:04PM +0200, Sergio Paracuellos wrote:
> Request for I/O resources from device tree call 'pci_remap_iospace' from
> 'devm_pci_remap_iospace' which is also called from device tree function
> 'pci_parse_request_of_pci_ranges'. if PCI_IOBASE is not defined and I/O
> resources are requested the following warning appears:
> 
> ------------[ cut here ]------------
> WARNING: CPU: 2 PID: 1 at ../drivers/pci/pci.c:4066 pci_remap_iospace+0x3c/0x54
> This architecture does not support memory mapped I/O
> Modules linked in:
> CPU: 2 PID: 1 Comm: swapper/0 Not tainted 5.10.1+ #1228
> Stack : 00000000 00000000 807fa974 00000000 827ffa80 80066b48 80710000 0000000b
>         00000000 00000000 81c59aac 7d06ddec 80850000 00000001 81c59a40 7d06ddec
>         00000000 00000000 807c909c 81c598f0 00000001 81c59904 00000000 0000000a
>         203a6d6d 80708880 0000000f 70617773 80850000 00000000 00000000 807d0000
>         807ffecc 1e160000 00000001 00000200 00000000 8054e920 00000008 815e0008
>         ...
> Call Trace:
> [<80008efc>] show_stack+0x8c/0x130
> [<806e1674>] dump_stack+0x9c/0xc8
> [<80024a3c>] __warn+0xc0/0xe8
> [<80024ad0>] warn_slowpath_fmt+0x6c/0xbc
> [<80410ca8>] pci_remap_iospace+0x3c/0x54
> [<80410d20>] devm_pci_remap_iospace+0x58/0xa4
> [<8042019c>] devm_of_pci_bridge_init+0x4dc/0x55c
> [<80408de8>] devm_pci_alloc_host_bridge+0x78/0x88
> [<80424e44>] mt7621_pci_probe+0x68/0x9a4
> [<80464804>] platform_drv_probe+0x40/0x7c
> [<804628bc>] really_probe+0x2fc/0x4e4
> [<80463214>] device_driver_attach+0x4c/0x74
> [<80463384>] __driver_attach+0x148/0x150
> [<8046047c>] bus_for_each_dev+0x6c/0xb0
> [<804614dc>] bus_add_driver+0x1b4/0x1fc
> [<80463aa0>] driver_register+0xd0/0x110
> [<80001714>] do_one_initcall+0x84/0x1c0
> [<808e7fd0>] kernel_init_freeable+0x214/0x24c
> [<806e4164>] kernel_init+0x14/0x118
> [<80003358>] ret_from_kernel_thread+0x14/0x1c
> 
> ---[ end trace 1c9d4412bd51b53c ]---
> mt7621-pci 1e140000.pcie: error -19: failed to map resource [io  0x1e160000-0x1e16ffff]
> 
> Since there are architectures (like MIPS ralink) that can request I/O
> resources from device tree but have not mapeable I/O space and also PCI_IOBASE
> not defined, avoid this warning and just return zero to make the I/O ranges
> assignment work.
> 
> Signed-off-by: Sergio Paracuellos <sergio.paracuellos@gmail.com>
> ---
>  drivers/pci/pci.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index aacf575c15cf..10bb2191f376 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -4102,9 +4102,9 @@ unsigned long __weak pci_address_to_pio(phys_addr_t address)
>   * @phys_addr: physical address of range to be mapped
>   *
>   * Remap the memory mapped I/O space described by the @res and the CPU
> - * physical address @phys_addr into virtual address space.  Only
> - * architectures that have memory mapped IO functions defined (and the
> - * PCI_IOBASE value defined) should call this function.
> + * physical address @phys_addr into virtual address space. There
> + * are architectures that don't define PCI_IOBASE but can have not
> + * mapeable IO space. Return zero for those cases.
>   */
>  int pci_remap_iospace(const struct resource *res, phys_addr_t phys_addr)
>  {
> @@ -4122,10 +4122,10 @@ int pci_remap_iospace(const struct resource *res, phys_addr_t phys_addr)
>  #else
>  	/*
>  	 * This architecture does not have memory mapped I/O space,
> -	 * so this function should never be called
> +	 * but can have not mapeable I/O space, so just return ok
> +	 * here.
>  	 */
> -	WARN_ONCE(1, "This architecture does not support memory mapped I/O\n");
> -	return -ENODEV;
> +	return 0;

This doesn't seem right to me.  pci_remap_iospace() remaps
memory-mapped I/O space into virtual address space.

If the architecture doesn't support that remapping, we shouldn't claim
that it succeeded.

The analogous path for ACPI is in acpi_pci_root_remap_iospace(), where
we only call pci_remap_iospace() if PCI_IOBASE is defined.  Maybe we
should use the same approach here, i.e., add the corresonding #ifdef
in pci_parse_request_of_pci_ranges()?

>  #endif
>  }
>  EXPORT_SYMBOL(pci_remap_iospace);
> -- 
> 2.25.1
>