netdev - Re: [Intel-wired-lan] [PATCH next-queue v5 3/4] igc: Enable PCIe PTM

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Message-ID: <87r1havm15.fsf@vcostago-mobl2.amr.corp.intel.com>
Date:   Wed, 09 Jun 2021 13:08:22 -0700
From:   Vinicius Costa Gomes <vinicius.gomes@...el.com>
To:     Paul Menzel <pmenzel@...gen.mpg.de>
Cc:     linux-pci@...r.kernel.org, richardcochran@...il.com,
        hch@...radead.org, netdev@...r.kernel.org, bhelgaas@...gle.com,
        helgaas@...nel.org, intel-wired-lan@...ts.osuosl.org
Subject: Re: [Intel-wired-lan] [PATCH next-queue v5 3/4] igc: Enable PCIe PTM

Paul Menzel <pmenzel@...gen.mpg.de> writes:

> Dear Vinicius,
>
>
> Am 08.06.21 um 21:02 schrieb Vinicius Costa Gomes:
>
>> Paul Menzel writes:
>
>>> Am 05.06.21 um 02:23 schrieb Vinicius Costa Gomes:
>>>> Enables PCIe PTM (Precision Time Measurement) support in the igc
>>>> driver. Notifies the PCI devices that PCIe PTM should be enabled.
>>>>
>>>> PCIe PTM is similar protocol to PTP (Precision Time Protocol) running
>>>> in the PCIe fabric, it allows devices to report time measurements from
>>>> their internal clocks and the correlation with the PCIe root clock.
>>>>
>>>> The i225 NIC exposes some registers that expose those time
>>>> measurements, those registers will be used, in later patches, to
>>>> implement the PTP_SYS_OFFSET_PRECISE ioctl().
>>>>
>>>> Signed-off-by: Vinicius Costa Gomes <vinicius.gomes@...el.com>
>>>> ---
>>>>    drivers/net/ethernet/intel/igc/igc_main.c | 6 ++++++
>>>>    1 file changed, 6 insertions(+)
>>>>
>>>> diff --git a/drivers/net/ethernet/intel/igc/igc_main.c b/drivers/net/ethernet/intel/igc/igc_main.c
>>>> index a05e6d8ec660..f23d0303e53b 100644
>>>> --- a/drivers/net/ethernet/intel/igc/igc_main.c
>>>> +++ b/drivers/net/ethernet/intel/igc/igc_main.c
>>>> @@ -12,6 +12,8 @@
>>>>    #include <net/pkt_sched.h>
>>>>    #include <linux/bpf_trace.h>
>>>>    #include <net/xdp_sock_drv.h>
>>>> +#include <linux/pci.h>
>>>> +
>>>>    #include <net/ipv6.h>
>>>>    
>>>>    #include "igc.h"
>>>> @@ -5864,6 +5866,10 @@ static int igc_probe(struct pci_dev *pdev,
>>>>    
>>>>    	pci_enable_pcie_error_reporting(pdev);
>>>>    
>>>> +	err = pci_enable_ptm(pdev, NULL);
>>>> +	if (err < 0)
>>>> +		dev_err(&pdev->dev, "PTM not supported\n");
>>>> +
>>>
>>> Sorry, if I am missing something, but do all devices supported by this
>>> driver support PTM or only the i225 NIC? In that case, it wouldn’t be an
>>> error for a device not supporting PTM, would it?
>> 
>> That was a very good question. I had to talk with the hardware folks.
>> All the devices supported by the igc driver should support PTM.
>
> Thank you for checking that, that is valuable information.
>
>> And just to be clear, the reason that I am not returning an error here
>> is that PTM could not be supported by the host system (think PCI
>> controller).
>
> I just checked `pci_enable_ptm()` and on success it calls 
> `pci_ptm_info()` logging a message:
>
> 	pci_info(dev, "PTM enabled%s, %s granularity\n",
> 		 dev->ptm_root ? " (root)" : "", clock_desc);
>
> Was that present on your system with your patch? Please add that to the 
> commit message.

Yes, with my patches applied I can see this message on my systems.

Sure, will add this to the commit message.

>
> Regarding my comment, I did not mean returning an error but the log 
> *level* of the message. So, `dmesg --level err` would show that message. 
> But if there are PCI controllers not supporting that, it’s not an error, 
> but a warning at most. So, I’d use:
>
> 	dev_warn(&pdev->dev, "PTM not supported by PCI bus/controller 
> (pci_enable_ptm() failed)\n");

I will use you suggestion for the message, but I think that warn is a
bit too much, info or notice seem to be better.


Cheers,
-- 
Vinicius