linux-kernel - Re: [PATCH v10 07/10] OF: Introduce helper function for getting PCI domain

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Date:	Wed, 10 Sep 2014 14:04:32 +0100
From:	Liviu Dudau <Liviu.Dudau@....com>
To:	Rob Herring <robherring2@...il.com>
Cc:	Bjorn Helgaas <bhelgaas@...gle.com>, Arnd Bergmann <arnd@...db.de>,
	Rob Herring <robh+dt@...nel.org>,
	Jason Gunthorpe <jgunthorpe@...idianresearch.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Catalin Marinas <Catalin.Marinas@....com>,
	Will Deacon <Will.Deacon@....com>,
	Russell King <linux@....linux.org.uk>,
	linux-pci <linux-pci@...r.kernel.org>,
	Linus Walleij <linus.walleij@...aro.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>,
	linux-arch <linux-arch@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Device Tree ML <devicetree@...r.kernel.org>,
	LAKML <linux-arm-kernel@...ts.infradead.org>,
	"grant.likely@...aro.org" <grant.likely@...aro.org>
Subject: Re: [PATCH v10 07/10] OF: Introduce helper function for getting PCI
 domain_nr

On Mon, Sep 08, 2014 at 04:59:31PM +0100, Liviu Dudau wrote:
> On Mon, Sep 08, 2014 at 04:27:36PM +0100, Rob Herring wrote:
> > On Mon, Sep 8, 2014 at 9:54 AM, Liviu Dudau <Liviu.Dudau@....com> wrote:
> > > On Mon, Sep 08, 2014 at 03:27:56PM +0100, Rob Herring wrote:
> > >> On Mon, Sep 8, 2014 at 8:54 AM, Liviu Dudau <Liviu.Dudau@....com> wrote:
> > >> > Add of_pci_get_domain_nr() to retrieve the PCI domain number
> > >> > of a given device from DT. If the information is not present,
> > >> > the function can be requested to allocate a new domain number.
> > >> >
> > >> > Cc: Bjorn Helgaas <bhelgaas@...gle.com>
> > >> > Cc: Arnd Bergmann <arnd@...db.de>
> > >> > Cc: Grant Likely <grant.likely@...aro.org>
> > >> > Cc: Rob Herring <robh+dt@...nel.org>
> > >> > Reviewed-by: Catalin Marinas <catalin.marinas@....com>
> > >> > Signed-off-by: Liviu Dudau <Liviu.Dudau@....com>
> > >> > ---
> > >> >  drivers/of/of_pci.c    | 34 ++++++++++++++++++++++++++++++++++
> > >> >  include/linux/of_pci.h |  7 +++++++
> > >> >  2 files changed, 41 insertions(+)
> > >> >
> > >> > diff --git a/drivers/of/of_pci.c b/drivers/of/of_pci.c
> > >> > index 8481996..a107edb 100644
> > >> > --- a/drivers/of/of_pci.c
> > >> > +++ b/drivers/of/of_pci.c
> > >> > @@ -89,6 +89,40 @@ int of_pci_parse_bus_range(struct device_node *node, struct resource *res)
> > >> >  }
> > >> >  EXPORT_SYMBOL_GPL(of_pci_parse_bus_range);
> > >> >
> > >> > +static atomic_t of_domain_nr = ATOMIC_INIT(-1);
> > >> > +
> > >> > +/**
> > >> > + * This function will try to obtain the host bridge domain number by
> > >> > + * using of_alias_get_id() call with "pci-domain" as a stem. If that
> > >> > + * fails, a local allocator will be used. The local allocator can
> > >> > + * be requested to return a new domain_nr if the information is missing
> > >> > + * from the device tree.
> > >> > + *
> > >> > + * @node: device tree node with the domain information
> > >> > + * @allocate_if_missing: if DT lacks information about the domain nr,
> > >> > + * allocate a new number.
> > >> > + *
> > >> > + * Returns the associated domain number from DT, or a new domain number
> > >> > + * if DT information is missing and @allocate_if_missing is true. If
> > >> > + * @allocate_if_missing is false then the last allocated domain number
> > >> > + * will be returned.
> > >> > + */
> > >> > +int of_pci_get_domain_nr(struct device_node *node, bool allocate_if_missing)
> > >> > +{
> > >> > +       int domain;
> > >> > +
> > >> > +       domain = of_alias_get_id(node, "pci-domain");
> > >> > +       if (domain == -ENODEV) {
> > >> > +               if (allocate_if_missing)
> > >> > +                       domain = atomic_inc_return(&of_domain_nr);
> > >> > +               else
> > >> > +                       domain = atomic_read(&of_domain_nr);
> > >>
> > >> This function seems a bit broken to me. It is overloaded with too many
> > >> different outcomes. Think about how this would work if you have
> > >> multiple PCI buses and a mixture of having pci-domain aliases or not.
> > >> Aren't domain numbers global? Allocation should then start outside of
> > >> the range of alias ids.
> > >>
> > >> Rob
> > >>
> > >
> > > Rob,
> > >
> > > Would this version make more sense?
> > 
> > No.
> > 

Hi Rob,

Here is an updated version of the patch. I have implemented a separate function
for getting the max domain number from the device tree and use the result as
the start value + 1 for the allocator.

Best regards,
Liviu

-- 
====================
| I would like to |
| fix the world,  |
| but they're not |
| giving me the   |
 \ source code!  /
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View attachment "0001-OF-Introduce-helper-function-for-getting-PCI-domain_.patch" of type "text/x-diff" (4100 bytes)