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Date: Fri, 3 Mar 2023 15:28:55 -0800
From: Jakub Kicinski <kuba@...nel.org>
To: Köry Maincent <kory.maincent@...tlin.com>
Cc: "Russell King (Oracle)" <linux@...linux.org.uk>,
Richard Cochran <richardcochran@...il.com>, andrew@...n.ch,
davem@...emloft.net, f.fainelli@...il.com, hkallweit1@...il.com,
netdev@...r.kernel.org,
Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
Maxime Chevallier <maxime.chevallier@...tlin.com>
Subject: Re: [PATCH RFC net-next] net: phy: add Marvell PHY PTP support
[multicast/DSA issues]
On Fri, 3 Mar 2023 14:12:47 +0100 Köry Maincent wrote:
> > Do you happen to have a datasheet for MACB? The time stamping
> > capability is suspiciously saved in a variable called hw_dma_cap
> > which may indicate it's a DMA time stamp not a true PTP stamp.
> >
> > Quite a few NICs/MACs support DMA time stamps because it's far
> > easier to take the stamp where the descriptor writing logic is
> > (DMA block) than take it at the end of the MAC and haul it all
> > the way thru the pipeline back to the DMA block.
>
> I don't have the datasheet but indeed you seem to have right. From the support
> commit message:
> > Time stamps are obtained from the dma buffer descriptors
That's just saying that the time stamp is communicated via
a descriptor rather than a register, so not a strong proof
of where it's taken.
> I suppose it is less precise as using true PTP stamp as it is an hardware block
> further. Is that right?
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