netdev - Re: [PATCH RFC net-next] net: phy: add Marvell PHY PTP support [multicast/DSA issues]

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Date:   Fri, 3 Mar 2023 14:12:47 +0100
From:   Köry Maincent <kory.maincent@...tlin.com>
To:     Jakub Kicinski <kuba@...nel.org>
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 Thu, 2 Mar 2023 09:23:20 -0800
Jakub Kicinski <kuba@...nel.org> 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

I suppose it is less precise as using true PTP stamp as it is an hardware block
further. Is that right?

Regards,
Köry