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

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Date:	Mon, 7 Apr 2014 09:31:20 +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 Sat, Apr 05, 2014 at 01:19:53AM +0100, Bjorn Helgaas wrote:
> On Fri, Mar 14, 2014 at 03:34:27PM +0000, Liviu Dudau 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.
> 
> It's true that the current Linux "x86 view of PCI I/O space" is pretty
> simple and limited.  But I don't think that's a fundamental x86 limitation
> (other than the fact that the actual INB/OUTB/etc. CPU instructions
> themselves are limited to a single 64K I/O port space).

Hi Bjorn,

Thanks for reviewing this series.

I might've taken a too dim view of x86 world. I tend to split the existing
architectures into the ones that have special I/O instructions and the ones
that map a region of memory into CPU space and do I/O transactions there as
simple read/writes.

> 
> Host bridges on x86 could have MMIO apertures that turn CPU memory accesses
> into PCI port accesses.  We could implement any number of I/O port spaces
> this way, by making the kernel inb()/outb()/etc. interfaces smart enough to
> use the memory-mapped space instead of (or in addition to) the
> INB/OUTB/etc. instructions.

Right, sorry for my ignorance then: how does *currently* the device driver do
the I/O transfer transparent of the implementation mechanism? Or they have
intimate knowledge of wether the device is behind a host bridge and can do MMIO
or is on an ISA or CF bus and then it needs INB/OUTB ? And if we make inb/outb
smarter, does that mean that we need to change the drivers?

> 
> ia64 does this (see arch/ia64/include/asm/io.h for a little description)
> and I think maybe one or two other arches have something similar.
> 
> > 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.
> 
> I don't quite see how you intend to use this, because this series doesn't
> include any non-stub implementation of pci_register_io_range().
> 
> Is this anything like the ia64 strategy I mentioned above?  If so, it would
> be really nice to unify some of this stuff.

After discussions with Arnd and Catalin I know have a new series that moves
some of the code from arm64 series into this one. I am putting it through
testing right know as I am going to have to depend on another series that
makes PCI_IOBASE defined only for architectures that do MMIO in order to
choose the correct default implementation for these functions. My hope is
that I will be able to send the series this week.

Best regards,
Liviu

> 
> > 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
> > +}
> > +
> >  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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