Re: [net-next PATCH 0/8] configuration support for switch headers & phy

[Hariprasad Kelam]

> -----Original Message-----
> From: Andrew Lunn <andrew@xxxxxxx>
> Sent: Sunday, March 28, 2021 11:17 PM
> To: Sunil Kovvuri <sunil.kovvuri@xxxxxxxxx>
> Cc: Hariprasad Kelam <hkelam@xxxxxxxxxxx>; netdev@xxxxxxxxxxxxxxx;
> linux-kernel@xxxxxxxxxxxxxxx; kuba@xxxxxxxxxx; davem@xxxxxxxxxxxxx;
> Sunil Kovvuri Goutham <sgoutham@xxxxxxxxxxx>; Linu Cherian
> <lcherian@xxxxxxxxxxx>; Geethasowjanya Akula <gakula@xxxxxxxxxxx>;
> Jerin Jacob Kollanukkaran <jerinj@xxxxxxxxxxx>; Subbaraya Sundeep Bhatta
> <sbhatta@xxxxxxxxxxx>
> Subject: [EXT] Re: [net-next PATCH 0/8] configuration support for switch
> headers & phy
> 
> > 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 ?
> 
> Hi Sunil
> 
> 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 the
> {E}DSA protocol used by Marvell switches, or even that the switch is a
> Marvell switch.
> 
> netdev_uses_dsa(ndev) will tell you if the MAC is being used to connect to 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 hard
> to use, since you don't have a clear indicator when to evaluate to determine
> if you need to change your packet parsing.
> 
> netdev_uses_dsa() looks at ndev->dsa_ptr. This is a pointer to the structure
> 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 gives
> 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. And
> this is all within the core DSA code, so is generic. It should work for any
> tagging protocol used by any switch which Linux DSA supports.
> 
> So actually, everything you need is already present, you don't need a private
> flag. But adding a notifier that the MAC has been connected to a switch and
> 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 back once we have clear picture.

Thanks,
Hariprasad k 
> 
>       Andrew