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

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Date:	Mon, 8 Sep 2014 15:54:59 +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 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?

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);
       } else {
               /* remember the largest value seen */
               int d = atomic_read(&of_domain_nr);
               atomic_set(&of_domain_nr, max(domain, d));
       }

       return domain;
}
EXPORT_SYMBOL_GPL(of_pci_get_domain_nr);

It would still create gaps and possible duplicates, but this is just a number
and trying to create a new root bus in an existing domain should fail. I have
no clue on how to generate unique values without parsing the DT and filling
a sparse array with values found there and then checking for allocated values
on new requests. This function gets called quite a lot and I'm trying not to
make it too heavy weight.


Best regards,
Liviu

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

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