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

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Message-ID: <d8740484-3879-1c13-65ce-82d3e71cb96c@molgen.mpg.de>
Date:   Wed, 9 Jun 2021 23:26:09 +0200
From:   Paul Menzel <pmenzel@...gen.mpg.de>
To:     Vinicius Costa Gomes <vinicius.gomes@...el.com>
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

Dear Vinicius,


Am 09.06.21 um 22:08 schrieb Vinicius Costa Gomes:
> Paul Menzel writes:

>> 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.

I do not know, if modern PCI(e)(?) controllers normally support PTM or 
not. If recent controllers should support it, then a warning would be 
warranted, otherwise a notice.


Kind regards,

Paul