linux-kernel - Re: [PATCH] arm64: Add architecture support for PCI

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Message-ID: <20140203191837.GC4889@e106497-lin.cambridge.arm.com>
Date:	Mon, 3 Feb 2014 19:18:38 +0000
From:	Liviu Dudau <Liviu.Dudau@....com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	linux-pci <linux-pci@...r.kernel.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Catalin Marinas <Catalin.Marinas@....com>,
	Will Deacon <Will.Deacon@....com>,
	LKML <linux-kernel@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	LAKML <linux-arm-kernel@...ts.infradead.org>,
	linaro-kernel <linaro-kernel@...ts.linaro.org>
Subject: Re: [PATCH] arm64: Add architecture support for PCI

On Mon, Feb 03, 2014 at 06:58:56PM +0000, Arnd Bergmann wrote:
> On Monday 03 February 2014 18:43:48 Liviu Dudau wrote:
> > diff --git a/arch/arm64/include/asm/io.h b/arch/arm64/include/asm/io.h
> > index 4cc813e..ce5bad2 100644
> > --- a/arch/arm64/include/asm/io.h
> > +++ b/arch/arm64/include/asm/io.h
> > @@ -120,9 +120,13 @@ static inline u64 __raw_readq(const volatile void __iomem *addr)
> >  /*
> >   *  I/O port access primitives.
> >   */
> > +#define arch_has_dev_port()	(0)
> 
> Why not?

Maybe I got it the wrong way around, but the comment in include/linux/io.h says:

/*
 * Some systems do not have legacy ISA devices.
 * /dev/port is not a valid interface on these systems.
 * So for those archs, <asm/io.h> should define the following symbol.
 */

So ... defining it should mean no legacy ISA devices, right?

> 
> >  #define IO_SPACE_LIMIT		0xffff
> 
> You probably want to increase this a bit, to allow multiple host bridges
> to have their own I/O space.

OK, but to what size?

> 
> >  #define PCI_IOBASE		((void __iomem *)(MODULES_VADDR - SZ_2M))
> 
> And modify this location: There is no particular reason to have the I/O space
> mapped exactly 2MB below the loadable modules, as virtual address space is
> essentially free.

Will talk with Catalin about where to place this.

> 
> > +#define ioport_map(port, nr)	(PCI_IOBASE + ((port) & IO_SPACE_LIMIT))
> > +#define ioport_unmap(addr)
> 
> inline functions?

Will do, thanks!

> 
> >  static inline u8 inb(unsigned long addr)
> >  {
> >  	return readb(addr + PCI_IOBASE);
> > diff --git a/arch/arm64/include/asm/pci.h b/arch/arm64/include/asm/pci.h
> > new file mode 100644
> > index 0000000..dd084a3
> > --- /dev/null
> > +++ b/arch/arm64/include/asm/pci.h
> > @@ -0,0 +1,35 @@
> > +#ifndef __ASM_PCI_H
> > +#define __ASM_PCI_H
> > +#ifdef __KERNEL__
> > +
> > +#include <linux/types.h>
> > +#include <linux/slab.h>
> > +#include <linux/dma-mapping.h>
> > +
> > +#include <asm/io.h>
> > +#include <asm-generic/pci-bridge.h>
> > +#include <asm-generic/pci-dma-compat.h>
> > +
> > +#define PCIBIOS_MIN_IO		0
> > +#define PCIBIOS_MIN_MEM		0
> 
> PCIBIOS_MIN_IO is normally set to 0x1000, to stay out of the ISA range.

:) No ISA support! (Die ISA, die!!) 

> 
> > diff --git a/arch/arm64/kernel/pci.c b/arch/arm64/kernel/pci.c
> > new file mode 100644
> > index 0000000..7b652cf
> > --- /dev/null
> > +++ b/arch/arm64/kernel/pci.c
> > @@ -0,0 +1,112 @@
> 
> None of this looks really arm64 specific, nor should it be. I think
> we should try a little harder to move this as a default implementation
> into common code, even if we start out by having all architectures
> override it.

Agree. This is the RFC version. I didn't dare to post a patch with fixes
for all architectures. :)

> 
> > +int pci_ioremap_io(unsigned int offset, phys_addr_t phys_addr)
> > +{
> > +	BUG_ON(offset + SZ_64K - 1 > IO_SPACE_LIMIT);
> > +
> > +	return ioremap_page_range((unsigned long)PCI_IOBASE + offset,
> > +				(unsigned long)PCI_IOBASE + offset + SZ_64K,
> > +				phys_addr,
> > +				__pgprot(PROT_DEVICE_nGnRE));
> > +}
> 
> Not sure if we want to treat this one as architecture specific though.
> It certainly won't be portable to x86, but it could be shared with
> a couple of others. We may also want to redesign the interface.
> I've been thinking we could make this function allocate space in the
> Linux virtual I/O space aperture, and pass two resources into it
> (physical I/O aperture and bus I/O range), and get the actual
> io_offset as the return value, or a negative error number.

Not sure I completely follow your idea.

> 
> That way, you could have an arbitrary number of host bridges in the
> system and each one gets a share of the virtual aperture until
> it's full.

One still needs to fix the pci_request_region use that checks against
ioport_resource. But it is an interesting idea.

> 
> 	Arnd
> 
> 

Thanks for reviewing this patch!

Liviu

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

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