netdev - Re: [PATCH v3 1/1 net-next] net: fec: enable pause frame to improve rx prefomance for 1G network

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Date:	Thu, 24 Jan 2013 16:49:33 +0000
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	Frank Li <lznuaa@...il.com>
CC:	Frank Li <Frank.Li@...escale.com>, <shawn.guo@...aro.org>,
	<B38611@...escale.com>, <davem@...emloft.net>,
	<linux-arm-kernel@...ts.infradead.org>, <netdev@...r.kernel.org>,
	<s.hauer@...gutronix.de>
Subject: Re: [PATCH v3 1/1 net-next] net: fec: enable pause frame to improve
 rx prefomance for 1G network

On Thu, 2013-01-24 at 10:16 +0800, Frank Li wrote:
> 2013/1/24 Ben Hutchings <bhutchings@...arflare.com>:
> > On Thu, 2013-01-17 at 10:55 +0800, Frank Li wrote:
> >> The limition of imx6 internal bus cause fec can't achieve 1G perfomance.
> >> There will be many packages lost because FIFO over run.
> >>
> >> This patch enable pause frame flow control.
> > [...]
> >> --- a/drivers/net/ethernet/freescale/fec.c
> >> +++ b/drivers/net/ethernet/freescale/fec.c
> > [...]
> >> +static int fec_enet_set_pauseparam(struct net_device *ndev,
> >> +                                struct ethtool_pauseparam *pause)
> >> +{
> >> +     struct fec_enet_private *fep = netdev_priv(ndev);
> >> +
> >> +     if (pause->tx_pause != pause->rx_pause) {
> >> +             netdev_info(ndev,
> >> +                     "hardware only support enable/disable both tx and rx");
> >> +             return -EINVAL;
> >> +     }
> >> +
> >> +     fep->pause_flag = 0;
> >> +
> >> +     /* tx pause must be same as rx pause */
> >> +     fep->pause_flag |= pause->rx_pause ? FEC_PAUSE_FLAG_ENABLE : 0;
> >> +     fep->pause_flag |= pause->autoneg ? FEC_PAUSE_FLAG_AUTONEG : 0;
> >> +
> >> +     if (pause->rx_pause || pause->autoneg) {
> >> +             fep->phy_dev->supported |= ADVERTISED_Pause;
> >> +             fep->phy_dev->advertising |= ADVERTISED_Pause;
> >> +     } else {
> >> +             fep->phy_dev->supported &= ~ADVERTISED_Pause;
> >> +             fep->phy_dev->advertising &= ~ADVERTISED_Pause;
> >> +     }
> > [...]
> >
> > Why is this changing the supported flags, i.e. device capabilities?  You
> > need to leave those flags alone and reject an attempt to enable pause
> > frames on a device that doesn't support them.
> 
> I go through phylib, I have not found good place set ADVERTISED_Pause
> capabilities.
> genphy_config_init never check Pause capabilities.

I agree that phylib can't initialise pause capabilities because those
depend on the MAC.  But look at which function I'm quoting: this is the
ethtool operation, which shouldn't change capabilities.

Ben.

-- 
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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