linux-kernel - Re: [PATCH v7 1/6] pci: Introduce pci_register_io

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Date:	Tue, 8 Apr 2014 10:49:33 +0100
From:	Liviu Dudau <Liviu.Dudau@....com>
To:	Bjorn Helgaas <bhelgaas@...gle.com>
Cc:	linux-pci <linux-pci@...r.kernel.org>,
	Catalin Marinas <Catalin.Marinas@....com>,
	Will Deacon <Will.Deacon@....com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	linaro-kernel <linaro-kernel@...ts.linaro.org>,
	Arnd Bergmann <arnd@...db.de>,
	LKML <linux-kernel@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	LAKML <linux-arm-kernel@...ts.infradead.org>,
	Tanmay Inamdar <tinamdar@....com>,
	Grant Likely <grant.likely@...retlab.ca>
Subject: Re: [PATCH v7 1/6] pci: Introduce pci_register_io_range() helper
 function.

On Tue, Apr 08, 2014 at 12:21:51AM +0100, Bjorn Helgaas wrote:
> On Fri, Mar 14, 2014 at 9:34 AM, Liviu Dudau <Liviu.Dudau@....com> wrote:
> > Some architectures do not share x86 simple view of the PCI I/O space
> > and instead use a range of addresses that map to bus addresses. For
> > some architectures these ranges will be expressed by OF bindings
> > in a device tree file.
> >
> > Introduce a pci_register_io_range() helper function that can be used
> > by the architecture code to keep track of the I/O ranges described by the
> > PCI bindings. If the PCI_IOBASE macro is not defined that signals
> > lack of support for PCI and we return an error.
> >
> > Signed-off-by: Liviu Dudau <Liviu.Dudau@....com>
> > Acked-by: Grant Likely <grant.likely@...aro.org>
> > Tested-by: Tanmay Inamdar <tinamdar@....com>
> > ---
> >  drivers/of/address.c       | 9 +++++++++
> >  include/linux/of_address.h | 1 +
> >  2 files changed, 10 insertions(+)
> >
> > diff --git a/drivers/of/address.c b/drivers/of/address.c
> > index 1a54f1f..be958ed 100644
> > --- a/drivers/of/address.c
> > +++ b/drivers/of/address.c
> > @@ -619,6 +619,15 @@ const __be32 *of_get_address(struct device_node *dev, int index, u64 *size,
> >  }
> >  EXPORT_SYMBOL(of_get_address);
> >
> > +int __weak pci_register_io_range(phys_addr_t addr, resource_size_t size)
> > +{
> > +#ifndef PCI_IOBASE
> > +       return -EINVAL;
> > +#else
> > +       return 0;
> > +#endif
> > +}
> 
> This isn't PCI code, so I'm fine with it in that sense, but I'm not
> sure the idea of a PCI_IOBASE #define is really what we need.  It's
> not really determined by the processor architecture, it's determined
> by the platform.  And a single address isn't enough in general,
> either, because if there are multiple host bridges, there's no reason
> the apertures that generate PCI I/O transactions need to be contiguous
> on the CPU side.

It should not be only platform's choice if the architecture doesn't support it.
To my mind PCI_IOBASE means "I support MMIO operations and this is the
start of the virtual address where my I/O ranges are mapped." It's the
same as ppc's _IO_BASE. And pci_address_to_pio() will take care to give
you the correct io_offset in the presence of multiple host bridges,
while keeping the io resource in the range [0 .. host_bridge_io_range_size - 1]

> 
> That's just a long way of saying that if we ever came up with a more
> generic way to handle I/O port spaces, PCI_IOBASE might go away.  And
> I guess part of that rework could be changing this use of it along
> with the others.

And I have a patch series that #defines PCI_IOBASE only in those architectures
that support MMIO, where this macro makes sense. Also notice that the
arm64 series has a patch that I'm going to roll into this one where ioport_map()
gets fixed to include PCI_IOBASE when !CONFIG_GENERIC_MAP.

Best regards,
Liviu

> 
> >  unsigned long __weak pci_address_to_pio(phys_addr_t address)
> >  {
> >         if (address > IO_SPACE_LIMIT)
> > diff --git a/include/linux/of_address.h b/include/linux/of_address.h
> > index 5f6ed6b..40c418d 100644
> > --- a/include/linux/of_address.h
> > +++ b/include/linux/of_address.h
> > @@ -56,6 +56,7 @@ extern void __iomem *of_iomap(struct device_node *device, int index);
> >  extern const __be32 *of_get_address(struct device_node *dev, int index,
> >                            u64 *size, unsigned int *flags);
> >
> > +extern int pci_register_io_range(phys_addr_t addr, resource_size_t size);
> >  extern unsigned long pci_address_to_pio(phys_addr_t addr);
> >
> >  extern int of_pci_range_parser_init(struct of_pci_range_parser *parser,
> > --
> > 1.9.0
> >
> 

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

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