netdev - Re: [PATCH] net/fec: call netif_carrier

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Date:	Fri, 26 Jul 2013 12:52:17 +0200
From:	Sascha Hauer <s.hauer@...gutronix.de>
To:	Florian Fainelli <florian@...nwrt.org>
Cc:	Duan Fugang-B38611 <B38611@...escale.com>,
	Stephen Hemminger <stephen@...workplumber.org>,
	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Estevam Fabio-R49496 <r49496@...escale.com>,
	Li Frank-B20596 <B20596@...escale.com>,
	Shawn Guo <shawn.guo@...aro.org>,
	"kernel@...gutronix.de" <kernel@...gutronix.de>,
	Hector Palacios <hector.palacios@...i.com>,
	Tim Sander <tim.sander@....com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] net/fec: call netif_carrier_off when not having link

On Fri, Jul 26, 2013 at 11:06:06AM +0100, Florian Fainelli wrote:
> Hello,
> 
> 2013/7/26 Duan Fugang-B38611 <B38611@...escale.com>:
> > On Fir, 26 Jul 2013 12:04, Stephen Hemminger wrote:
> >>> diff --git a/drivers/net/ethernet/freescale/fec_main.c
> >>> b/drivers/net/ethernet/freescale/fec_main.c
> >>> index 0642006..631bd5a 100644
> >>> --- a/drivers/net/ethernet/freescale/fec_main.c
> >>> +++ b/drivers/net/ethernet/freescale/fec_main.c
> >>> @@ -280,11 +280,6 @@ fec_enet_start_xmit(struct sk_buff *skb, struct net_device *ndev)
> >>>      unsigned short  status;
> >>>      unsigned int index;
> >>>
> >>> -    if (!fep->link) {
> >>> -            /* Link is down or auto-negotiation is in progress. */
> >>> -            return NETDEV_TX_BUSY;
> >>> -    }
> >>> -
> >>
> >>That is a bug anyway. Since it would cause spin loop in transmit code (even without -rt).
> >>If the driver cared to test it (most drivers just let hardware deal with this situation),
> >>then it should free packet and return TX_OK.
> >
> > When link is down, the logic is
> >         - call netif_stop_queue() to stop queue
> >         - and then notify there have no link using netif_carrier_off().
> 
> netif_carrier_off() is handled by the PHY library before calling the
> adjust_link callback in FEC.
> 
> >
> > But the flow must be handled in fec_enet_adjust_link() function, not in xmit().
> 
> What is special about this hardware that fec_restart() needs to do all
> that work?

The special thing is that the driver is written in a braindamaged way.
fec_restart is kind of a suicide-and-resurrect function which is called
whenever something changes.

> Can't you just update the duplex/speed/pause settings
> directly without doing a full hardware re-init?

Yes, that's possible. I made some initial patches for this which we'll
probably send soon.

Sascha


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