Re: [PATCH v7 3/3] arm64: Add architecture support for PCI

[Liviu Dudau <Liviu.Dudau@arm.com>]

On Thu, Mar 20, 2014 at 11:17:22AM +0000, Arnd Bergmann wrote:
> On Thursday 20 March 2014, Liviu Dudau wrote:
> > On Wed, Mar 19, 2014 at 06:37:51PM +0000, Arnd Bergmann wrote:
> > > On Wednesday 19 March 2014 17:21:41 Liviu Dudau wrote:
> > > > 
> > > > My ultimate point is that no matter how long we argue about the shape of the functions that
> > > > I've added into arch/arm64/kernel/pci.c I don't think we can get away without having that
> > > > file, or at least not in the first phase if we want speedy integration into mainline.
> > > 
> > > Let me simplify the discussion here:
> > > 
> > > NAK to adding yet another architecture specific implementation.
> > 
> > So what would be your approach for handling pci_address_to_pio() in a non-arch specific way?
> > 
> > unsigned long __weak pci_address_to_pio(phys_addr_t address)
> > {
> > #ifdef ARCH_HAS_IOSPACE
> >         if (address > IO_SPACE_LIMIT)
> >                 return (unsigned long)-1;
> > 
> >         return (unsigned long) address;
> > #else
> >         struct ioresource *res;
> > 
> >         list_for_each_entry(res, &io_list, list) {
> >                 if (address >= res->start &&
> >                         address < res->start + res->size) {
> >                         return res->start - address;
> >                 }
> >         }
> > 
> >         return (unsigned long)-1;
> > #endif
> > }
> > 
> > 
> > Either that, or you have more magic rabbits than me.
> 
> I don't even understand why you want to create a generic pci_address_to_pio
> implementation, when we don't need that for arm64 at all. Unless I'm
> missing something important, that function is only called in case of
> PCI_PROBE_DEVTREE with pci_of_scan on PowerPC. I don't expect any
> architecture to do the same thing, and the only other architecture that
> needs something like it (sparc) has a different implementation.

Because in my [v7 2/6]* patch for the generic host bridge support I start
using pci_address_to_pio to fix the conversion of PCI ranges to resources.
That requires an arm64 (or more correctly, an arch with memory mapped IO
specific) version of pci_address_to_pio().

Best regards,
Liviu

> 
> The regular (non-DEVTREE) PCI bus scan should just be able to translate
> the BUS I/O addresses into Linux I/O port numbers using io_offset,
> without going through an intermediate step of translating into a CPU
> physical address first, so the entire lookup method won't get used.
> 
> The reason why PowerPC needs it is that they traditionally don't
> use PCI config space access to assign or look at resources, but
> instead rely on the firmware to have set it up in advance and then
> put matching information into DT and the BARs. For Solaris and AIX,
> it's probably easier to use the information from DT, but in Linux,
> we already need to implement the manual bus scan, e.g. to do
> PCI device hotplugging if nothing else.
> 
> 	Arnd
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