linux-kernel - Re: [net-next PATCH] octeontx2: Add PTP clock driver for Octeon PTM clock.

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Date: Mon, 29 Jan 2024 17:31:12 -0800
From: Vinicius Costa Gomes <vinicius.gomes@...el.com>
To: Sai Krishna Gajula <saikrishnag@...vell.com>, "richardcochran@...il.com"
 <richardcochran@...il.com>, "davem@...emloft.net" <davem@...emloft.net>,
 "kuba@...nel.org" <kuba@...nel.org>, "netdev@...r.kernel.org"
 <netdev@...r.kernel.org>, "linux-kernel@...r.kernel.org"
 <linux-kernel@...r.kernel.org>, Sunil Kovvuri
 Goutham <sgoutham@...vell.com>, Geethasowjanya Akula <gakula@...vell.com>,
 Linu Cherian <lcherian@...vell.com>, Hariprasad Kelam
 <hkelam@...vell.com>, Subbaraya Sundeep Bhatta <sbhatta@...vell.com>
Cc: Naveen Mamindlapalli <naveenm@...vell.com>
Subject: Re: [net-next PATCH] octeontx2: Add PTP clock driver for Octeon PTM
 clock.

Sai Krishna Gajula <saikrishnag@...vell.com> writes:

>> -----Original Message-----
>> From: Vinicius Costa Gomes <vinicius.gomes@...el.com>
>> Sent: Friday, January 26, 2024 5:41 AM
>> To: Sai Krishna Gajula <saikrishnag@...vell.com>;
>> richardcochran@...il.com; davem@...emloft.net; kuba@...nel.org;
>> netdev@...r.kernel.org; linux-kernel@...r.kernel.org; Sunil Kovvuri
>> Goutham <sgoutham@...vell.com>; Geethasowjanya Akula
>> <gakula@...vell.com>; Linu Cherian <lcherian@...vell.com>; Hariprasad
>> Kelam <hkelam@...vell.com>; Subbaraya Sundeep Bhatta
>> <sbhatta@...vell.com>
>> Cc: Sai Krishna Gajula <saikrishnag@...vell.com>; Naveen Mamindlapalli
>> <naveenm@...vell.com>
>> Subject: Re: [net-next PATCH] octeontx2: Add PTP clock driver for
>> Octeon PTM clock.
>> 
>> Sai Krishna <saikrishnag@...vell.com> writes:
>> 
>> > The PCIe PTM(Precision time measurement) protocol provides precise
>> > coordination of events across multiple components like PCIe host
>> > clock, PCIe EP PHC local clocks of PCIe devices. This patch adds
>> > support for ptp clock based PTM clock. We can use this PTP device to
>> > sync the PTM time with CLOCK_REALTIME or other PTP PHC devices using
>> > phc2sys.
>> >
>> > Signed-off-by: Sai Krishna <saikrishnag@...vell.com>
>> > Signed-off-by: Naveen Mamindlapalli <naveenm@...vell.com>
>> > Signed-off-by: Sunil Kovvuri Goutham <sgoutham@...vell.com>
>> > ---
>> 
>> I can see that the same device id (PCI_DEVID_OCTEONTX2_PTP) is used by a
>> ethernet driver.
>> 
>> That brings me a question: why expose a different PTP chardev? In other
>> words, why can't you just implement .getcrosststamp() for that ethernet
>> device?
>
> This driver runs on endpoint device and not on the host.
> getcrosststamp() needs ART time, frequency details in case of x86 host
> system. Our use case is to sync the host's PTP/PTM time to the
> endpoint device via PTM interface.

Ah! I see. This is for "the other side", cool :-)

Cheers,
-- 
Vinicius