RE: [PATCH net-next] net: hns3: Add support to change MTU in hardware & netdev

[Salil Mehta]

Hi Andrew

> -----Original Message-----
> From: Andrew Lunn [mailto:andrew@xxxxxxx]
> Sent: Friday, August 18, 2017 5:02 PM
> To: Salil Mehta
> Cc: davem@xxxxxxxxxxxxx; Zhuangyuzeng (Yisen); lipeng (Y);
> mehta.salil.lnk@xxxxxxxxx; netdev@xxxxxxxxxxxxxxx; linux-
> kernel@xxxxxxxxxxxxxxx; linux-rdma@xxxxxxxxxxxxxxx; Linuxarm
> Subject: Re: [PATCH net-next] net: hns3: Add support to change MTU in
> hardware & netdev
> 
> > for example,
> > file: drivers/net/ethernet/chelsio/cxgb4/cxgb4_main.c
> > static int init_one(struct pci_dev *pdev, const struct pci_device_id
> *ent)
> >
> >  		netdev->priv_flags |= IFF_UNICAST_FLT;
> >
> > +		/* MTU range: 81 - 9600 */
> > +		netdev->min_mtu = 81;
> > +		netdev->max_mtu = MAX_MTU;
> 
> In this cause, the driver is not using the default values. So it sets
> them.
> 
> Anyway, try it. After your alloc_etherdev_mqs(), print the value of
> min_mtu. It should already be set to MIN_ETH_MTU.
I understand your point. In this case, I would like to keep the
range being set by the driver just to be more explicit. 
So for now keep this initialization in the driver?

Thanks
Salil
> 
> > I see. IMHO HNS3 is currently limited by maximum buffer per
> descriptor
> > which is 64k. I am sure such frames would get dropped in the hardware
> > itself and which I guess should be more preferable than dropping in
> > driver since it saves you some precious cpu cycles?
> 
> If you hardware handles this, then you don't need to do anything.
Fine. Thanks!

Salil
> 
>    Andrew