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From:   Hariprasad Kelam <hkelam@marvell.com>
To:     Andrew Lunn <andrew@lunn.ch>,
        Sunil Kovvuri <sunil.kovvuri@gmail.com>
CC:     "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
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        Sunil Kovvuri Goutham <sgoutham@marvell.com>,
        Linu Cherian <lcherian@marvell.com>,
        Geethasowjanya Akula <gakula@marvell.com>,
        Jerin Jacob Kollanukkaran <jerinj@marvell.com>,
        Subbaraya Sundeep Bhatta <sbhatta@marvell.com>
Subject: Re: [net-next PATCH 0/8] configuration support for switch headers &
 phy
Thread-Topic: [net-next PATCH 0/8] configuration support for switch headers &
 phy
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Date:   Wed, 31 Mar 2021 14:36:19 +0000
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> -----Original Message-----
> From: Andrew Lunn <andrew@lunn.ch>
> Sent: Sunday, March 28, 2021 11:17 PM
> To: Sunil Kovvuri <sunil.kovvuri@gmail.com>
> Cc: Hariprasad Kelam <hkelam@marvell.com>; netdev@vger.kernel.org;
> linux-kernel@vger.kernel.org; kuba@kernel.org; davem@davemloft.net;
> Sunil Kovvuri Goutham <sgoutham@marvell.com>; Linu Cherian
> <lcherian@marvell.com>; Geethasowjanya Akula <gakula@marvell.com>;
> Jerin Jacob Kollanukkaran <jerinj@marvell.com>; Subbaraya Sundeep Bhatta
> <sbhatta@marvell.com>
> Subject: [EXT] Re: [net-next PATCH 0/8] configuration support for switch
> headers & phy
>=20
> > The usecase is simple, unlike DSA tag, this 4byte FDSA tag doesn't
> > have a ethertype, so HW cannot recognize this header. If such packers
> > arise, then HW parsing will fail and RSS will not work.
> >
> > Hypothetically if we introduce some communication between MAC driver
> > and DSA driver, wouldn't that also become specific to the device, what
> > generic usecase that communication will have ?
>=20
> Hi Sunil
>=20
> We need to be careful with wording. Due to history, the Linux kernel uses
> dsa to mean any driver to control an Ethernet switch. It does not imply t=
he
> {E}DSA protocol used by Marvell switches, or even that the switch is a
> Marvell switch.
>=20
> netdev_uses_dsa(ndev) will tell you if the MAC is being used to connect t=
o a
> switch. It is set by the Linux DSA core when the switch cluster is setup.=
 That
> could be before or after the MAC is configured up, which makes it a bit h=
ard
> to use, since you don't have a clear indicator when to evaluate to determ=
ine
> if you need to change your packet parsing.
>=20
> netdev_uses_dsa() looks at ndev->dsa_ptr. This is a pointer to the struct=
ure
> which represents the port on the switch the MAC is connected to. In Linux
> DSA terms, this is the CPU port. You can follow dsa_ptr->tag_ops which gi=
ves
> you the tagger operations, i.e. those used to add and remove the
> header/trailer. One member of that is proto. This contains the tagging
> protocol, so EDSA, DSA, or potentially FDSA, if that is ever supported. A=
nd
> this is all within the core DSA code, so is generic. It should work for a=
ny
> tagging protocol used by any switch which Linux DSA supports.
>=20
> So actually, everything you need is already present, you don't need a pri=
vate
> flag. But adding a notifier that the MAC has been connected to a switch a=
nd
> ndev->dsa_ptr is set would be useful. We could maybe use NETDEV_CHANGE
> for that, or NETDEV_CHANGELOWERSTATE, since the MAC is below the
> switch slave interfaces.


Hi Andrew,
	We are looking into  DSA to MAC driver communication options, will get bac=
k once we have clear picture.

Thanks,
Hariprasad k=20
>=20
>       Andrew