Re: [PATCH v8 1/3] perf: cavium: Support memory controller PMU counters

From: David Daney <ddaney.cavm@gmail.com>
To: Greg KH <gregkh@linuxfoundation.org>, Borislav Petkov <bp@alien8.de>
Cc: Mark Rutland <mark.rutland@arm.com>,
	Suzuki K Poulose <Suzuki.Poulose@arm.com>,
	linux-pci@vger.kernel.org, Will Deacon <will.deacon@arm.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Jan Glauber <jan.glauber@caviumnetworks.com>,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v8 1/3] perf: cavium: Support memory controller PMU counters
Date: Wed, 26 Jul 2017 13:02:38 -0700	[thread overview]
Message-ID: <1a2eedea-040d-c746-eaf0-1d8085b3f2bf@gmail.com> (raw)
In-Reply-To: <20170726173353.GB21705@kroah.com>

On 07/26/2017 10:33 AM, Greg KH wrote:
> On Wed, Jul 26, 2017 at 06:30:49PM +0200, Borislav Petkov wrote:
>> On Wed, Jul 26, 2017 at 09:19:49AM -0700, Greg KH wrote:
>>> On Wed, Jul 26, 2017 at 05:55:48PM +0200, Borislav Petkov wrote:
>>>> On Wed, Jul 26, 2017 at 05:45:15PM +0200, Jan Glauber wrote:
>>>>> The PMU/EDAC devices are all PCI devices do I need the 'struct pci_dev *'.
>>>>> I'm not aware of other ways to access these devices. Please enlighten
>>>>> me if I'm missing something.
>>>>
>>>> Me enlighten you on Cavium hardware?! You're funny.
>>>>
>>>> So I don't know whether the PCI hotplug code can run more than one
>>>> function upon PCI ID detection. Probably Greg will say, write a
>>>> multiplexer wrapper. :-)
>>>
>>> -ENOCONTEXT....
>>>
>>> Anyway, pci questions are best asked on the linux-pci@vger list.  And
>>> yes, all PCI devices end up with a 'struct pci_dev *' automatically.
>>
>> Simple: so they have a PCI ID of a memory contoller and want to hotplug
>> two drivers for it. And those two drivers should remain independent from
>> each other.
> 
> Hahahahaha, no.  That's crazy, you were right in guessing what my answer
> was going to be :)
> 

Just to be clear about the situation, the device is a memory controller. 
  It has two main behaviors we are interested in:

A) Error Detection And Correction (EDAC).  This should be connected to 
the kernel's EDAC subsystem.  An existing driver 
(drivers/edac/thunderx_edac.c) does exactly this.

B) Performance Counters for actions taken in the corresponding memory. 
This should be connected to the kernel's perf framework as an uncore-PMU 
(the subject of this patch set).

It is a single PCI device.  What should the driver architecture look 
like to connect it to two different kernel subsystems?

Thanks,
David Daney

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