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

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Message-ID: <939b8042-a313-47db-43d9-ea37e95b724b@molgen.mpg.de>
Date:   Wed, 9 Jun 2021 08:24:18 +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 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.

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");

>>>    	pci_set_master(pdev);
>>>    
>>>    	err = -ENOMEM;


Kind regards,

Paul