linux-kernel - Re: [PATCH v2 1/4] pci: OF: Fix the conversion of IO ranges into IO resources.

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Date:	Fri, 28 Feb 2014 12:50:45 +0000
From:	Liviu Dudau <Liviu.Dudau@....com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Jason Gunthorpe <jgunthorpe@...idianresearch.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	linux-pci <linux-pci@...r.kernel.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Catalin Marinas <Catalin.Marinas@....com>,
	Will Deacon <Will.Deacon@....com>,
	linaro-kernel <linaro-kernel@...ts.linaro.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/4] pci: OF: Fix the conversion of IO ranges into IO
 resources.

On Thu, Feb 27, 2014 at 08:22:12PM +0000, Arnd Bergmann wrote:
> On Thursday 27 February 2014 13:07:29 Jason Gunthorpe wrote:
> > On Thu, Feb 27, 2014 at 08:48:08PM +0100, Arnd Bergmann wrote:
> > > > It also looks correct for architectures that use the CPU MMIO address
> > > > as the IO address directly (where IO_SPACE_LIMIT would be 4G)
> > > 
> > > Are you aware of any that still do? I thought we had stopped doing
> > > that.
> > 
> > I thought ia64 used to, but it has been a long time since I've touched
> > one...
> 
> They have a different way of doing it now, no idea how it looked in
> the past:
> 
> #define IO_SPACE_LIMIT          0xffffffffffffffffUL
> 
> #define MAX_IO_SPACES_BITS              8
> #define MAX_IO_SPACES                   (1UL << MAX_IO_SPACES_BITS)
> #define IO_SPACE_BITS                   24
> #define IO_SPACE_SIZE                   (1UL << IO_SPACE_BITS)
> 
> #define IO_SPACE_NR(port)               ((port) >> IO_SPACE_BITS)
> #define IO_SPACE_BASE(space)            ((space) << IO_SPACE_BITS)
> #define IO_SPACE_PORT(port)             ((port) & (IO_SPACE_SIZE - 1))
> 
> #define IO_SPACE_SPARSE_ENCODING(p)     ((((p) >> 2) << 12) | ((p) & 0xfff))
> 
> So their port number is a logical token that contains the I/O space number
> and a 16MB offset.
> 
> Apparently sparc64 uses physical memory addressing for I/O space, the
> same way they do for memory space, and they just set IO_SPACE_LIMIT to
> 0xffffffffffffffffUL.
> 
> > > > Architectures that use the virtual IO window technique will always
> > > > require a custom pci_address_to_pio implementation.
> > > 
> > > Hmm, at the moment we only call it from of_address_to_resource(),
> > > which in turn does not get called on PCI devices, and does not
> > > call pci_address_to_pio for 'simple' platform devices. The only
> > > case I can think of where it actually matters is when we have
> > > ISA devices in DT that use an I/O port address in the reg property,
> > > and that case hopefully won't happen on ARM32 or ARM64.
> > 
> > Sure, I ment, after Liviu's patch it will become required since he is
> > cleverly using it to figure out what the io mapping the bridge driver
> > setup before calling the helper.
> 
> Ok. I was arguing more that we should add this dependency.

I've thought about this last night and I think I was trying to be too clever
for my own good. As Jason points out, arm64 needs its own version of
pci_address_to_pio(). I have an idea on how to borrow the powerpc/microblaze
one and make it useful without the need for pci_controller *hose. It would
be generic enough for other platforms that use virtual I/O windows can use,
but I'll start with it being defined for arm64 for discussions in this list.

I'll post v3 shortly.

Best regards,
Liviu

> 
> > > > I think the legacy reasons for having all those layers of translation
> > > > are probably not applicable to ARM64, and it is much simpler without
> > > > the extra translation step....
> > > > 
> > > > Arnd, what do you think?
> > > 
> > > Either I don't like it or I misunderstand you ;-)
> > > 
> > > Most PCI drivers normally don't call ioport_map or pci_iomap, so
> > > we can't just do it there. If you are thinking of calling ioport_map
> > 
> > Okay, that was one of the 'legacy reasons'. Certainly lots of drivers
> > do call pci_iomap, but if you think legacy drivers that don't are
> > important to ARM64 then it makes sense to use the virtual IO window.
> 
> I think all uses of I/O space are legacy, but I don't think that
> drivers doing inb/outb are more obsolete than those doing pci_iomap.
> It's got more to do with the subsystem requirements, e.g. libata
> requires the use of pci_iomap.
> 
> > > for every PCI device that has an I/O BAR and storing the virtual
> > > address in the pci_dev resource, I don't see what that gains us
> > 
> > Mainly we get to drop the fancy dynamic allocation stuff for the fixed
> > virtual window, and it gives the option to have a 1:1 relationship
> > between CPU addresses and PCI BARs.
> 
> I don't think the allocation is much of a problem, as long as we
> can localize it in one function that is shared by everyone.
> The problems I saw were all about explaining to people how it
> works, but they really shouldn't have to know.
> 
> 
> 	Arnd
> 
> 

-- 
====================
| I would like to |
| fix the world,  |
| but they're not |
| giving me the   |
 \ source code!  /
  ---------------
    ¯\_(ツ)_/¯

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