linux-kernel - Re: [PATCH 1/2] nios2: Add architectural support for PCIe

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Date:	Tue, 22 Sep 2015 13:42:28 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Ley Foon Tan <lftan@...era.com>
Cc:	Bjorn Helgaas <bhelgaas@...gle.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Linux-Arch <linux-arch@...r.kernel.org>,
	linux-pci@...r.kernel.org
Subject: Re: [PATCH 1/2] nios2: Add architectural support for PCIe

On Tuesday 22 September 2015 18:53:50 Ley Foon Tan wrote:
> On Tue, Sep 22, 2015 at 4:18 PM, Arnd Bergmann <arnd@...db.de> wrote:
> > On Tuesday 22 September 2015 15:19:26 Ley Foon Tan wrote:
> > I might be missing something though. Bjorn?
> >
> >> @@ -14,7 +14,7 @@
> >>  #include <linux/types.h>
> >>  #include <asm/pgtable-bits.h>
> >>
> >> -/* PCI is not supported in nios2, set this to 0. */
> >> +/* PCI I/O space is not supported, set this to 0. */
> >>  #define IO_SPACE_LIMIT 0
> >>
> >>  #define readb_relaxed(addr)  readb(addr)
> >
> > It might be useful to enable this, just in case someone connects
> > a PCI host bridge that does support I/O space.
> >
> > Which host bridge do you use? Are you sure there is no I/O space?
> > Most of them use a set of translation windows to set up a mapping
> > between bus address (memory, config and io space) and physical
> > (mmio) space.
>
> I'm using Altera PCIe IP. But, you are right. We should enable this,
> because it shouldn't limited to support Altera PCIe only.
> BTW, any rule/requirement for the IO_SPACE_LIMIT?

If you want to allow just one PCI host bridge, set it to 0xffff, otherwise
use 0xfffff (for up to 16 bridges)

> And PCIBIOS_MIN_IO should be non-zero if we enable IO_SPACE_LIMIT?

If you define pcibios_align_resource() as an empty function, that can
remain zero as well, it's only meant to stay out of the way of ISA
devices.

> >> diff --git a/arch/nios2/include/asm/pci.h b/arch/nios2/include/asm/pci.h
> >> new file mode 100644
> >> index 0000000..f2cba05
> >> --- /dev/null
> >> +++ b/arch/nios2/include/asm/pci.h
> >
> > What happens if you use the asm-generic header? If there is something
> > missing in it, we can try to get it to do the right things.
> All the defines in arch/nios2/include/asm/pci.h are required by PCI framework.
> It will trigger undefined symbols/define error if without them. Seem
> all architectures must provide all these defines.
> So, we can consider to add default defines for these in asm-generic.

I think that would be good, yes. We probably picked defaults for the
asm-generic version that are enough to build with CONFIG_PCI disabled,
but there are useful defaults for the other case as well.

Most architectures that use the file don't support PCI, so you can just
add stuff inside of #ifdef CONFIG_PCI. For the remaining 13 architectures
(git grep -l generic/pci.h  | wc), see whether there are conflicts first.
The normal way would be to have the arch specific definition come before
the #include, and then do something like

#ifndef pci_proc_domain
#define pci_proc_domain pci_proc_domain
static inline int pci_proc_domain(struct pci_bus *bus)
{
#ifdef CONFIG_PCI_DOMAINS_GENERIC
        return pci_domain_nr(bus);
#else
	return 1;
}
#endif

	Arnd
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