linux-kernel - Re: [PATCH V2 00/23] MMCONFIG refactoring and support for ARM64 PCI hostbridge init based on ACPI

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Date:	Tue, 12 Jan 2016 22:37:54 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Lorenzo Pieralisi <lorenzo.pieralisi@....com>
Cc:	Sinan Kaya <okaya@...eaurora.org>,
	Tomasz Nowicki <tn@...ihalf.com>, bhelgaas@...gle.com,
	will.deacon@....com, catalin.marinas@....com, rjw@...ysocki.net,
	hanjun.guo@...aro.org, jiang.liu@...ux.intel.com,
	stefano.stabellini@...citrix.com,
	robert.richter@...iumnetworks.com, mw@...ihalf.com,
	liviu.dudau@....com, ddaney@...iumnetworks.com, tglx@...utronix.de,
	wangyijing@...wei.com, suravee.suthikulpanit@....com,
	msalter@...hat.com, linux-pci@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-acpi@...r.kernel.org,
	linux-kernel@...r.kernel.org, linaro-acpi@...ts.linaro.org,
	jchandra@...adcom.com, jcm@...hat.com
Subject: Re: [PATCH V2 00/23] MMCONFIG refactoring and support for ARM64 PCI hostbridge init based on ACPI

On Tuesday 12 January 2016 18:38:54 Lorenzo Pieralisi wrote:
> On Tue, Jan 12, 2016 at 03:30:25PM +0100, Arnd Bergmann wrote:
> > On Monday 11 January 2016 10:56:30 Sinan Kaya wrote:
> > > 
> > > #_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).

> > 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