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

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Date:   Fri, 21 Oct 2022 00:25:13 +0000
From:   "Zulkifli, Muhammad Husaini" <muhammad.husaini.zulkifli@...el.com>
To:     Richard Cochran <richardcochran@...il.com>
CC:     "intel-wired-lan@...osl.org" <intel-wired-lan@...osl.org>,
        "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>,
        "gal@...dia.com" <gal@...dia.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

Hi Richard,

> -----Original Message-----
> From: Richard Cochran <richardcochran@...il.com>
> Sent: Wednesday, 19 October, 2022 10:37 AM
> To: Zulkifli, Muhammad Husaini <muhammad.husaini.zulkifli@...el.com>
> Cc: intel-wired-lan@...osl.org; netdev@...r.kernel.org; kuba@...nel.org;
> davem@...emloft.net; edumazet@...gle.com; Gunasekaran, Aravindhan
> <aravindhan.gunasekaran@...el.com>; gal@...dia.com; saeed@...nel.org;
> leon@...nel.org; michael.chan@...adcom.com; 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 Tue, Oct 18, 2022 at 02:12:37PM +0000, Zulkifli, Muhammad Husaini
> wrote:
> > > What is the use case for reporting DMA transmit time?
> 
> So the use case (mentioned below) is TSN?

Yes. TSN/Real Time applications. The most desirable is reporting the HW Timestamp.
But if all real time applications in a heavy traffic load trying to use same 
HW Timestamp (ex. 1 HW Timestamp only available) there will be a failure event 
Like missing a timestamp. The purpose of DMA transmit time is to give the application 
a different option for using DMA Timestamp when this event occur.

> 
> > > How is this better than using SOF_TIMESTAMPING_TX_SOFTWARE ?
> >
> > The ideal situation is to use SOF TIMESTAMPING TX SOFTWARE.
> > Application side will undoubtedly want to utilize PHY timestamps as much
> as possible.
> 
> I'm asking about SOFTWARE not hardware time stamps.

Sorry for misinterpreting SOFTWARE as HARDWARE in my previous reply.
DMA Timestamping is definitely better than SOFTWARE timestamp because 
we sample the time at the controller MAC level.

> 
> > But if every application requested the HW Tx timestamp, especially
> > during periods of high load like TSN, in some cases when the controller only
> supports 1 HW timestamp, it would be a disaster.
> 
> But can't you offer 1 HW time stamp with many SW time stamps? 

Could you please provide additional details about this? What do you meant by 
offering 1 HW Timestamp with many SW timestamps? 

> 
> Thanks,
> Rihcard