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

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Date:   Thu, 27 Jul 2017 10:29:53 -0700
From:   David Daney <ddaney.cavm@...il.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     Borislav Petkov <bp@...en8.de>,
        Mark Rutland <mark.rutland@....com>,
        Suzuki K Poulose <Suzuki.Poulose@....com>,
        linux-pci@...r.kernel.org, Will Deacon <will.deacon@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Jan Glauber <jan.glauber@...iumnetworks.com>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v8 1/3] perf: cavium: Support memory controller PMU
 counters

On 07/26/2017 07:29 PM, Greg KH wrote:
> On Wed, Jul 26, 2017 at 02:02:42PM -0700, David Daney wrote:
>> On 07/26/2017 01:08 PM, Greg KH wrote:
>>> On Wed, Jul 26, 2017 at 01:02:38PM -0700, David Daney wrote:
>>>> 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@...r 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?
>>>
>>> Modify the drivers/edac/thunderx_edac.c code to add support for
>>> performance counters.
>>>
>>
>> Thanks Greg.  This adds some clarity to the situation.
>>
>> This technique does slightly complicate the mapping of files and directories
>> in the kernel source tree to maintainers.
>>
>> Also, if a given configuration disables CONFIG_EDAC there is some hackery
>> needed to get the perf portion of the driver included.
> 
> Well, you all deserve it for trying to have a single PCI device do
> multiple things at the same time.  There's no real good reason for
> creating hardware that way, PCI devices are "free", you should go throw
> a printed copy of the PCI spec at the firmware developers who did this
> to you.

The problem lies in something even more congealed than the "firmware". 
The PCI topology is etched in to the very fabric of the silicon of the SoC.


> 
> Then get them to fix the firmware so you have multiple PCI devices...
> 
> good luck!

We'll use all of that we can get!  Thanks.


> 
> greg k-h
>