linux-kernel - Re: [PATCH v8 2/9] pci: Export find_pci_host

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Date:	Wed, 2 Jul 2014 13:43:41 -0700
From:	Tanmay Inamdar <tinamdar@....com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Liviu Dudau <Liviu.Dudau@....com>,
	linux-pci <linux-pci@...r.kernel.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Catalin Marinas <Catalin.Marinas@....com>,
	Will Deacon <Will.Deacon@....com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	linaro-kernel <linaro-kernel@...ts.linaro.org>,
	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>,
	patches <patches@....com>
Subject: Re: [PATCH v8 2/9] pci: Export find_pci_host_bridge() function.

On Wed, Jul 2, 2014 at 12:12 PM, Arnd Bergmann <arnd@...db.de> wrote:
> On Wednesday 02 July 2014 11:06:38 Tanmay Inamdar wrote:
>> On Tue, Jul 1, 2014 at 11:43 AM, Liviu Dudau <Liviu.Dudau@....com> wrote:
>> > This is a useful function and we should make it visible outside the
>> > generic PCI code. Export it as a GPL symbol.
>> >
>> > Signed-off-by: Liviu Dudau <Liviu.Dudau@....com>
>> > Tested-by: Tanmay Inamdar <tinamdar@....com>
>> > ---
>> >  drivers/pci/host-bridge.c | 3 ++-
>> >  1 file changed, 2 insertions(+), 1 deletion(-)
>> >
>> > diff --git a/drivers/pci/host-bridge.c b/drivers/pci/host-bridge.c
>> > index 0e5f3c9..36c669e 100644
>> > --- a/drivers/pci/host-bridge.c
>> > +++ b/drivers/pci/host-bridge.c
>> > @@ -16,12 +16,13 @@ static struct pci_bus *find_pci_root_bus(struct pci_bus *bus)
>> >         return bus;
>> >  }
>> >
>> > -static struct pci_host_bridge *find_pci_host_bridge(struct pci_bus *bus)
>> > +struct pci_host_bridge *find_pci_host_bridge(struct pci_bus *bus)
>> >  {
>> >         struct pci_bus *root_bus = find_pci_root_bus(bus);
>> >
>> >         return to_pci_host_bridge(root_bus->bridge);
>> >  }
>> > +EXPORT_SYMBOL_GPL(find_pci_host_bridge);
>>
>> Is there any specific reason behind making this symbol GPL? I think
>> the other functions in this file are just EXPORT_SYMBOL. Ultimately
>> companies which have non gpl Linux modules (nvidia) will face issue
>> using this API.
>>
>> The same applies to 'of_create_pci_host_bridge'.
>
> I think EXPORT_SYMBOL_GPL() is better here. The new symbols are unlikely
> to be used by a peripheral device driver, and PCI host controllers are
> already restricted by EXPORT_SYMBOL_GPL.
>

You are right as long as the functions are not used directly. But what
if GPL functions are called indirectly.  For example, 'pci_domain_nr'
implementation in Liviu's V7 series calls 'find_pci_host_bridge'.

> nvidia will certainly not do a PCI host controller driver that is not
> upstream or not GPL-compatible.
>
>         Arnd
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