linux-kernel - Re: [PATCH 3/3] perf/x86/intel/uncore: Add Skylake server uncore support

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Date:	Wed, 17 Aug 2016 09:28:20 -0500
From:	Nilay Vaish <nilayvaish@...il.com>
To:	"Liang, Kan" <kan.liang@...el.com>
Cc:	"peterz@...radead.org" <peterz@...radead.org>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"mingo@...hat.com" <mingo@...hat.com>,
	Linux Kernel list <linux-kernel@...r.kernel.org>,
	"eranian@...gle.com" <eranian@...gle.com>,
	Andi Kleen <andi@...stfloor.org>
Subject: Re: [PATCH 3/3] perf/x86/intel/uncore: Add Skylake server uncore support

On 15 August 2016 at 09:12, Liang, Kan <kan.liang@...el.com> wrote:
>
>
>> > diff --git a/arch/x86/events/intel/uncore_snbep.c
>> > b/arch/x86/events/intel/uncore_snbep.c
>> > index 3719af5..55a081e 100644
>> > --- a/arch/x86/events/intel/uncore_snbep.c
>> > +++ b/arch/x86/events/intel/uncore_snbep.c
>> > +
>> > +static int skx_count_chabox(void)
>> > +{
>> > +       struct pci_dev *chabox_dev = NULL;
>> > +       int bus, count = 0;
>> > +
>> > +       while (1) {
>> > +               chabox_dev = pci_get_device(PCI_VENDOR_ID_INTEL, 0x208d,
>> chabox_dev);
>> > +               if (!chabox_dev)
>> > +                       break;
>> > +               if (count == 0)
>> > +                       bus = chabox_dev->bus->number;
>> > +               if (bus != chabox_dev->bus->number)
>> > +                       break;
>> > +               count++;
>> > +       }
>> > +
>> > +       pci_dev_put(chabox_dev);
>> > +       return count;
>> > +}
>>
>> Kan,  do we not need to call pci_dev_put() each time we call pci_get_device()?
>
> The pci_get_device will always decrease the reference count for chabox_dev, if
> it is not NULL.
> So I think it's OK to only pci_dev_put it at last.
>

Yup, you are right.  I was not aware that pci_dev_put() gets called
automatically when pci_dev argument is not NULL.
Thanks for the info.

--
Nilay