linux-kernel - Re: [PATCH v8 8/9] pci: Add support for creating a generic host

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Message-ID: <20140708225755.GE4980@e106497-lin.cambridge.arm.com>
Date:	Tue, 8 Jul 2014 23:57:55 +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>,
	Arnd Bergmann <arnd@...db.de>,
	linaro-kernel <linaro-kernel@...ts.linaro.org>,
	Tanmay Inamdar <tinamdar@....com>,
	Grant Likely <grant.likely@...retlab.ca>,
	Sinan Kaya <okaya@...eaurora.org>,
	Jingoo Han <jg1.han@...sung.com>,
	Kukjin Kim <kgene.kim@...sung.com>,
	Suravee Suthikulanit <suravee.suthikulpanit@....com>,
	LKML <linux-kernel@...r.kernel.org>,
	Device Tree ML <devicetree@...r.kernel.org>,
	LAKML <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v8 8/9] pci: Add support for creating a generic
 host_bridge from device tree

On Tue, Jul 08, 2014 at 11:37:37PM +0100, Bjorn Helgaas wrote:
> On Tue, Jul 08, 2014 at 11:27:38PM +0100, Liviu Dudau wrote:
> > On Tue, Jul 08, 2014 at 10:33:05PM +0100, Bjorn Helgaas wrote:
> > > On Tue, Jul 08, 2014 at 11:29:40AM +0100, Liviu Dudau wrote:
> > > > On Tue, Jul 08, 2014 at 02:01:04AM +0100, Bjorn Helgaas wrote:
> > > > > On Tue, Jul 01, 2014 at 07:43:33PM +0100, Liviu Dudau wrote:
> > > > > > ...
> > > > > > +int __weak pcibios_fixup_bridge_ranges(struct list_head *resources)
> > > > > > +{
> > > > > > +     return 0;
> > > > > > +}
> > > > > 
> > > > > I'd wait to add this until there's a platform that needs to implement it.
> > > > > Splitting it out will make this patch that much smaller and easier to
> > > > > understand.
> > > > 
> > > > I need this as this is the default implementation (i.e. do nothing). Otherwise the
> > > > link phase will give errors. 
> > > 
> > > I meant that you could remove the default implementation *and* the call of
> > > it, since it currently does nothing.
> > 
> > True. But it looks like converting Will's pci-host-generic.c driver will make use of this.
> 
> I think we should move this part of the patch to the conversion of
> that driver.  That will keep related changes grouped together, which 
> makes them easier to review and easier to backport, e.g., to distro
> kernels.
> 
> > > > > > diff --git a/include/linux/pci.h b/include/linux/pci.h
> > > > > > index 7e7b939..556dc5f 100644
> > > > > > --- a/include/linux/pci.h
> > > > > > +++ b/include/linux/pci.h
> > > > > > @@ -402,6 +402,7 @@ struct pci_host_bridge {
> > > > > >       struct device dev;
> > > > > >       struct pci_bus *bus;            /* root bus */
> > > > > >       int domain_nr;
> > > > > > +     resource_size_t io_base;        /* physical address for the start of I/O area */
> > > > > 
> > > > > I don't see where this is used yet.
> > > > 
> > > > It's used in pci_host_bridge_of_get_ranges() (earlier in this patch).
> > > 
> > > of_create_pci_host_bridge() fills in bridge->io_base, but I don't see
> > > anything that ever *reads* bridge->io_base.
> > 
> > Ah, understood. It is used by the host bridge drivers to set their ATR registers to the
> > correct CPU address values.
> 
> Same applies here.

Except I have no idea which host bridge driver is going to be submitted first. There are
at least a couple of public series for HB drivers based on my series plus the one I have yet
to submit for my platform.

Maybe an associated documentation patch that explains the intended use for io_base could
persuade you on the value of keeping the io_base patch here?

Best regards,
Liviu

> 
> Bjorn
> 

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

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