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

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Message-ID: <CAL_JsqJi8k1Goc3UmXhuxf9v7=4gJrYG_Di7v574PxS8TsJaXw@mail.gmail.com>
Date:	Mon, 8 Sep 2014 09:27:56 -0500
From:	Rob Herring <robherring2@...il.com>
To:	Liviu Dudau <Liviu.Dudau@....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 <grant.likely@...aro.org>
Subject: Re: [PATCH v10 07/10] OF: Introduce helper function for getting PCI domain_nr

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
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