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

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Date:   Tue, 08 Jun 2021 12:02:30 -0700
From:   Vinicius Costa Gomes <vinicius.gomes@...el.com>
To:     Paul Menzel <pmenzel@...gen.mpg.de>,
        intel-wired-lan@...ts.osuosl.org
Cc:     linux-pci@...r.kernel.org, richardcochran@...il.com,
        hch@...radead.org, netdev@...r.kernel.org, bhelgaas@...gle.com,
        helgaas@...nel.org
Subject: Re: [Intel-wired-lan] [PATCH next-queue v5 3/4] igc: Enable PCIe PTM

Hi Paul,

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

> Dear Vinicius,
>
>
> 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.

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).

>
>>   	pci_set_master(pdev);
>>   
>>   	err = -ENOMEM;
>> 
>
>
> Kind regards,
>
> Paul


Cheers,
-- 
Vinicius