netdev - Re: [PATCH v2 0/5] Add support for DMA timestamp for non-PTP packets

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Message-ID: <acb0cac6-17a9-3443-71f4-1f52b2186de7@nvidia.com>
Date:   Sun, 23 Oct 2022 10:15:06 +0300
From:   Gal Pressman <gal@...dia.com>
To:     "Zulkifli, Muhammad Husaini" <muhammad.husaini.zulkifli@...el.com>,
        "intel-wired-lan@...osl.org" <intel-wired-lan@...osl.org>
Cc:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        "Gunasekaran, Aravindhan" <aravindhan.gunasekaran@...el.com>,
        "richardcochran@...il.com" <richardcochran@...il.com>,
        "saeed@...nel.org" <saeed@...nel.org>,
        "leon@...nel.org" <leon@...nel.org>,
        "michael.chan@...adcom.com" <michael.chan@...adcom.com>,
        "andy@...yhouse.net" <andy@...yhouse.net>,
        "Gomes, Vinicius" <vinicius.gomes@...el.com>
Subject: Re: [PATCH v2 0/5] Add support for DMA timestamp for non-PTP packets

On 19/10/2022 17:23, Zulkifli, Muhammad Husaini wrote:
>>> DMA timestamps through socket options are not currently available to
>>> the user. Because if the user wants to, they can configure the
>>> hwtstamp config option to use the new introduced DMA Time Stamp flag
>>> through the setsockopt().
>>>
>>> With these additional socket options, users can continue to utilise HW
>>> timestamps for PTP while specifying non-PTP packets to use DMA
>>> timestamps if the NIC can support them.
>> Is it per socket?
> Yes it is per socket.
>
>> Will there be a way to know which types of timestamps are going to be used
>> on queues setup time?
> We can get the which timestamp that is supported through "ethtool -T" command.
> May I know why you want to know which timestamp need to configure during queue setup?

In mlx5 we need dedicated queues which support port timestamp. In
today's implementation we have a setup time priv-flag which dictates
whether these queues should be opened or not.

>
>>> This patch series also add a new HWTSTAMP_FILTER_DMA_TIMESTAMP
>> receive
>>> filters. This filter can be configured for devices that support/allow
>>> the DMA timestamp retrieval on receive side.
>> So if I understand correctly, to solve the problem you described at the
>> beginning, you'll disable port timestamp for all incoming packets? ptp
>> included?
> For ptp, it will always use Port Timestamp.
> Other application that want to use DMA Timestamp can request for the same.
>

How?
When a packet arrives from the wire the hardware doesn't know if it's
ptp or not. Does your hardware inspect the packet headers to decide when
to timestamp it?