On Tuesday 12 January 2016 18:38:54 Lorenzo Pieralisi wrote:

On Tue, Jan 12, 2016 at 03:30:25PM +0100, Arnd Bergmann wrote:

quoted

On Monday 11 January 2016 10:56:30 Sinan Kaya wrote:

quoted

#_dmesg_|_grep_resource
[    2.945762] pci_bus 0000:00: root bus resource [io  0x0000-0xefff window] (bus address [0x1000-0xffff])
[    3.652201] pci_bus 0002:00: root bus resource [io  0xf000-0x1dfff window] (bus address [0x1000-0xffff])
[    6.546716] pci_bus 0006:00: root bus resource [io  0x1e000-0x2cfff window] (bus address [0x1000-0xffff])
/ #

This is bad. We normally want to stay out of the first 0x1000 bytes of
the Linux space, to prevent drivers from poking into the ISA
registers.

You are referring to:

pci_bus 0000:00: root bus resource [io  0x0000-0xefff window]
                                        ^^^^^^
here, right ? [0x0 - PCIBIOS_MIN_IO] is not assigned by the PCI
code that reassigns resources anyway, so devices with IO BARs won't
get assigned [0x0 - PCIBIOS_MIN_IO] address space (Linux space).

Are you saying we should disallow the [0x0 - 0x1000] in the PCI busses
IO resource (Linux space) ?

In pci_address_to_pio() the offset (Linux IO resource) we assign starts
from 0x0, so we always allocate that chunk of IO address space (that is
an offset into the Linux virtual address space), am I correct ?

I think we can assign the address zero of the Linux I/O port range, but
we should never assign it to a bus port range that does not also start
at zero.

If we encounter a firmware description that has bus range which excludes
the first 1k, we should probably assign it to somewhere after 0x10000
(65536), so we can later assign a primary I/O space to a bus that has an
ISA or LPC bridge with actual devices below 0x1000 (4096).

quoted

We can have one of the buses be the "primary" bus that has its first
0x1000 bytes of I/O space mapped into the respective Linux addresses,
but mapping the second 0x1000 bytes into the reserved space is the
worst possible outcome here, as legacy ISA drivers will now poke at
random other devices that are intentionally moved to high addresses to
stay of of that range.

And you are referring to:

root bus resource [io  0x0000-0xefff window] (bus address [0x1000-0xffff])
		       ^^^^^^                              ^^^^^^

here ? If ISA drivers poke at addresses in the [0x0 - 0x1000]
range (Linux space IO offset) they end up on the PCI bus with addresses
above 0x1000, is that what you are saying when you refer to "moved to
high addresses to stay out of that range" ?

Correct.

	Arnd